QSO MUSEUM: A large atlas of cosmic structures surrounding high-redshift quasars

Figure 1. Nine of the targeted quasars (white circles) and the uncovered cosmic structures as seen in Lyman-alpha emission (blue-green). Each cut-out image is roughly 1 million light years in size. Credit: MPA/Jay Gonzalez Lobos, Fabrizio Arrigoni Battaia

Figure 2: Average surface brightness (top panel) and velocity dispersion (bottom panel) of the Lyman-alpha emission as a function of distance from each of the 120 targeted quasars. The curves are colour-coded according to the luminosity of each quasar. Credit: MPA/Jay Gonzalez Lobos

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Quasars are active supermassive black holes located at the centres of massive galaxies that emit energy levels that far exceed the binding energy of their host galaxies. This substantial amount of energy has the potential to impact the gas within and around the galaxies, thereby influencing their evolution. While the importance of this process is acknowledged, its details are still the subject of significant debate. An international team of researchers led by MPA scientists has now obtained observations of the most extensive sample of hydrogen structures surrounding quasars in the early universe to better understand this feedback process. The data reveal how the gas responds to the energy released by the supermassive black holes over distances of several hundred thousand light years, providing a new way to study the impact of quasars on galaxy evolution.

Quasar feedback plays a key role in shaping the evolution of the most massive galaxies in the universe. As the supermassive black hole at the centre of a galaxy accretes matter, it powers a quasar — a bright, energetic outburst that can blow powerful winds and emit radiation into the surrounding galaxy. This energy can either heat up or sweep away the gas that would otherwise form new stars, thereby effectively shutting down star formation. This explains why giant galaxies stop growing and become filled with older stars. However, in principle, a quasar is not only able to affect its host galaxy's interstellar medium (its local fuel reservoir), but also the surrounding intergalactic gas. This means that a quasar could have an impact also on the fresh fuel for future star formation in the galaxy, thereby accelerating the galaxy quenching. Despite these ideas have been extensively discussed, the details of this feedback process still need to be fully understood.

Since the 1980s, it has been proposed that the impact of quasar energy on the surrounding gas could be assessed by targeting one of the most important lines of the hydrogen atom: the Lyman-alpha line. In a hydrogen atom, the electron can occupy different energy levels, like steps on a ladder. This specific ultraviolet line is emitted when an electron drops from the second energy level to the first. Since hydrogen is the most abundant element in the universe, this transition is ubiquitous and results in such bright emission that it can be seen at distances of billions of light years, enabling us to study galaxies and their surrounding gas in the early universe. Novel wide-field spectrographs, in particular, have opened a new window on the Lyman-alpha emission surrounding quasars. They allow the detection of emitting gas at distances of several hundred thousand light years from their host galaxies with short exposure times (about one hour; see, for example, Highlights from November 2019, May 2022 and January 2025).

Thanks to this new instrumentation — specifically the integral-field spectrograph MUSE on the Very Large Telescope — an international team led by MPA scientists has surveyed the largest sample of quasars to date in order to study their surrounding Lyman-alpha emission. The observations revealed intricate structures enveloping these quasars during cosmic noon, an epoch corresponding to approximately 11.5 billion years ago (examples are shown in Figure 1). Importantly, the 120 targeted quasars cover two orders of magnitude in luminosity, enabling the team to explore the effects of different energy inputs.

The scientists discovered that the surface brightness of the Lyman-alpha emission — how bright the emission appears per unit angular area — depends on quasar luminosity. Brighter quasars are associated with brighter extended emission (see Figure 2, top panel). Similarly, brighter quasars are associated with more turbulent gas reservoirs within about 30 kpc (approximately 100,000 light years; see Figure 2, bottom panel). Both these trends are evidence of the impact of quasar feedback (radiation and winds) on their surroundings. The team is now quantifying these trends in detail. For example, they have found that the velocity dispersion on inner scales varies as a function of quasar luminosity, following a well-defined power law. These findings could be used to test quasar feedback models and how they couple with the gas. Future work will focus on targeting additional line emissions besides Lyman-alpha in order to further constrain the impact of quasars on the gas on such large scales, as well as the physical properties of the emitting gas (e.g. MPA Highlights July 2025).

 Source: Max Planck Institute for Astrophysics/Reasearch Highlghts

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Authors:

Jay González Lobos, Jay
PhD student
Tel: 2030
valegl@mpa-garching.mpg.de

Fabrizio Arrigoni Battaia
Scientific Staff
Tel: 2288
arrigoni@mpa-garching.mpg.de

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Original publication

Jay González Lobos, Fabrizio Arrigoni Battaia, Aura Obreja, Guinevere Kauffmann, Emanuele Paolo Farina, Tiago Costa

QSO MUSEUM III: the circumgalactic medium in Lyα emission around 120 z\sim3 quasars covering the SDSS parameter space. Witnessing the instantaneous AGN feedback on halo scales

Submitted to A&A

Source

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Gravitational Waves from Stars Stripped by Supermassive Black Holes?

Formation of the System

Cartoon of the system's key evolutionary stages. Top left: a binary enters the supermassive black hole's Hill sphere and is disrupted. One star is captured on an eccentric orbit, the other ejected as a hyper-velocity star. Top right: the captured star's orbit shrinks and circularizes via gravitational wave emission. Bottom left: the sub-giant star begins stable mass transfer onto the supermassive black hole. Bottom right: after losing its hydrogen envelope, the compact core continues inspiraling via gravitational wave emission, eventually becoming a loud LISA-band source. Adopted from Olejak et al. 2025.

Imagine a star not crashing into a supermassive black hole in a fiery explosion, but instead slowly spiraling in, circling closer and closer to its horizon. This is the story of a sub-giant star that is stripped of its hydrogen layer by a black hole companion with a few million solar masses. The left-over helium core is gently drawn in due to strong gravitational wave emission and can be placed so close to the supermassive black hole that it becomes a promising gravitational wave source for the future detector LISA (Laser Interferometer Space Antenna). This scenario has been recently investigated by a team at MPA.

The story begins with two stars in a binary system that drift too close to a supermassive black hole. The black hole’s powerful gravity tears them apart through the so-called Hills mechanism (see Fig. 1): One star is flung out at incredible speed (a so-called hyper-velocity star), while the other star is captured to orbit the black hole on a highly eccentric orbit. If the separation of the captured star is in a certain regime, gravitational waves will lead to gradual circularization and decay of the orbit (see Fig.1). As a consequence, the star will finally start to transfer mass onto the supermassive black hole on a relatively circular orbit.

If the captured star is a so called sub-giant, relatively soon after its main sequence phase (i.e. the end of its core hydrogen burning), it has already developed a helium core. Such a star may lose its outer layers to the supermassive black hole companion and be stripped – slowly but steadily – down to its helium-rich core (Fig.1).

Gravitational wave signal from a sub-giant (with initially 2 solar masses) transferring matter to a 4.3 million solar mass supermassive black hole, plotted against the gravitational wave frequency. The coloured curve shows the signal if the system is in the Milky Way, with time counting back from the final tidal disruption of the core (red star symbol). The colour scale indicates the signal-to-noise ratio of the gravitational wave signal, which can reach up to a million for the final disruption. Gray lines show more distant cases (up to 1 Gpc) and the solid black line (red dashed line) indicates the LISA sensitivity curve for a 4-year mission, showing that such a system would be detectable up to ~1 Gpc. Adopted from Olejak et al. 2025.

A Slow, Steady Spiral Inward

Unlike in the dramatic tidal disruption events often observed in galactic centers, where a star on a highly eccentric orbit might be ripped apart in one go, the mass transfer process investigated in this study happens over hundreds of thousands or millions of years. The star doesn’t disappear right away. Instead, it gradually loses mass, becoming a stripped helium core, and spirals inward.

Such a stripped core is compact enough that it can get very close to the supermassive black hole, at a separation comparable to the size of the black hole’s Schwarzschild radius. As the helium-core star slowly spirals in, it sends out a gravitational wave signal with gradually increasing frequency that space-based detectors like LISA are designed to pick up.

Moreover, every now and then, the core might light up again due to hydrogen reignition on the residual hydrogen-rich surface. Accompanying brief bursts of X-rays might be the visible sign of what’s happening – and a counterpart to the gravitational wave signal. If the spin of the supermassive black hole is sufficiently high, the final disruption of the helium core will happen near the so-called ‘innermost stable orbit’. This could be observable via both electromagnetic and gravitational wave emission, making it a very exciting multi-messenger transient.

These objects could be among the brightest gravitational wave sources in the Milky Way. Due to their loudness, they might also be detectable from large distances in the local Universe (see Fig. 2). In its several-year mission, LISA could detect dozens of them; hopefully even one right at the center of our own galaxy (with a chance of about 1%).

Illustration of a black hole stripping a star.
Credit: NASA/JPL-Caltech

A New Window into the Heart of Galaxies

The system described here is an example of a so-called ‘extreme mass ratio inspiral’ (due to the huge mass asymmetry between the star and the supermassive black hole). Such systems offer a unique opportunity to study the surroundings of supermassive black holes. Detecting one would not only shed light on how stars evolve in these exotic environments, but also on how they can feed black holes over extended timescales. Unlike typical interactions involving stellar-mass black holes, these systems may also produce short X-ray bursts from hydrogen flashes and end in a final tidal disruption.

This makes them promising candidates for multi-messenger astronomy, potentially linking gravitational wave signals with electromagnetic observations and offering a richer, more complete view of our universe.

Source: Max Planck Institute for Astrophysics

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Author:
Image of Dr. Aleksandra Olejak
Olejak, Aleksandra
Postdoc
tel:2231
aolejak@mpa-garching.mpg.de

Original publication

Aleksandra Olejak et al.
Supermassive Black Holes Stripping a Subgiant Star Down to Its Helium Core: A New Type of Multimessenger Source for LISA

2025 ApJL 987 L11

DOI

More Information

LISA
Website of the Laser Interferometer Space Antenna

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JWST's sharp view unveils intricate details in galaxies' gas halo

Fig. 1 Composite JWST image of the galaxy group SMM J02399-0136, which includes a quasar (circle), a dusty galaxy forming stars at very high rates (star sign) and an irregular satellite galaxy ("x" mark). The strong emission lines from doubly ionized oxygen (red) fall in one filter, and it is isolated by subtracting the image of stellar light (white) made from images of neighboring filters. It is compared to the hydrogen (blue) "nebula" obtained from Lyman alpha observations. © MPA

Fig. 2 Composite image and zoom-in view of the CGM gas. The main figure shows the star (white), oxygen (red), and radio jet (blue) emission around the galaxy group. Two scale bars denote 30,000 light-years, which is the distance between the Sun and the Milky Way center. The difference in the two directions is due to gravitational lensing. Zoomed views are shown of interesting regions, in a color scheme highlighting the oxygen emission. (a) Enlarged image of the disrupted satellite galaxy to the left of the quasar. The relativistic jet from the quasar (in blue) disrupts and strips the gas. The brightened region indicates where the jet interacts with the gas in the galaxy, whereas gas previously blown away from the satellite galaxy is seen as filaments further out. (b) A strong plume-like feature indicates a strong outflow from the quasar, and patchy remnant of previous outflows extends far to the right. (c) A long gas stream with a possible origin of inflow. (d) The "wave"-like structure, consisting of three parallel stripes, suggests episodic black hole activities and their feedback effects in the past. © MPA

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Galaxies are surrounded by a large reservoir of gas called the circumgalactic medium (CGM), where they refuel and recycle the gas for forming stars and growing in mass. This gas is extremely dim, with current observations being limited to spectral lines that are hard to interpret. It is therefore challenging to understand the mass, distribution, and physical conditions prevalent in the CGM. Recently, a group of researchers at MPA serendipitously discovered bright oxygen emission around a massive galaxy group in the distant universe using the James Webb Space Telescope (JWST). In collaboration with other international scientists and by combining various observations, the study provides a detailed and unprecedented view of the CGM, showing how galaxies influence the gas and their environment.

The well-known galaxy group SMM J02399-0136 includes a galaxy dominated by an active supermassive black hole, a dusty galaxy forming stars at very high rates, which is colliding with the quasar, and an irregular satellite galaxy (see Fig. 1). It is located at redshift 2.8 (when the universe was about 2.3 Gyr) and the galaxies appear gravitationally lensed in an east-west direction. Initially discovered due to its high star formation activity, later studies suggested a large reservoir of cool gas in atomic or molecular form in its CGM.

The new JWST observations offer the sharpest and one of the deepest views of the CGM gas. In particular there is strong oxygen emission ([O III]λ4959,5007Å), which extends at least 100 kpc (300,000 light-years) across its CGM. The oxygen distribution matches well with the hydrogen distribution revealed by previous Lyman alpha observations. Besides its vast extent, the image also uncovers a detailed filamentary structure of the CGM gas, resolved only by JWST (see zoomed images in Fig. 2).

The emission line of doubly ionized oxygen provides critical information. The bright emission indicates the presence of denser and warmer gas in the CGM than previously expected. Each of these long and narrow filaments contains a substantial gas mass, about a billion times the mass of the Sun, all in ionized form. Additionally, the large quantities of oxygen—produced only in stars and supernovae—compared to hydrogen in the CGM suggest that the CGM is chemically enriched by gas ejected from galaxies.

The bright filaments significantly contrast the "nebula" picture from previous studies. The high-resolution images show that the gas in the CGM is not distributed more or less uniformly, but rather resides in long and narrow filaments. The morphology, distribution, and oxygen abundance all point to past feedback from galaxy activities, which have fed mass, energy, and heavy elements into the CGM gas. Furthermore, the interaction between the quasar jet and the neighbouring galaxy is a striking example of how massive galaxies can impact their environments. These high-resolution images also challenge numerical simulations, which need to explain and reproduce the exquisitely complex structures revealed in this galaxy group.

The study demonstrates how CGM research can leverage the unprecedented resolution and sensitivity of the JWST, as well as the usefulness of oxygen lines in interpreting the gas's physical conditions. The research group is currently working on additional multi-wavelength data to construct a comprehensive understanding of various forms of gas in the CGM.

Source: Max Planck Institute for Astrophysics/Research Highlights

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Authors:

Bo Peng
Postdoc

Fabrizio Arrigoni Battaia
Scientific Staff
2288
arrigoni@mpa-garching.mpg.de

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Original publication

Direct high-resolution observation of feedback and chemical enrichment in the circumgalactic medium at redshift z ∼ 2.8
A&A, 694, L1 (2025)

Source | DOI

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Triple Stellar Systems as Gravitational Wave Sources

Scientific visualization of numerical relativity simulations showing gravitational waves emitted by inspiraling compact objects. Credit: T. Dietrich, S. Ossokine, H. Pfeiffer, and A. Buonanno (Max Planck Institute for Gravitational Physics).

A schematic diagram of possible key processes that drive the evolutionary phases of a triple evolution leading to the formation of double white dwarfs in the LISA frequency bandwidth. Depending on the separation of the inner binary and the inclination angle of the two orbital planes, the third star can interact in various ways with the inner binary. Just over half the systems retain the third star, though it is typically too distant to affect the gravitational wave signal significantly. © MPA

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Ground-based gravitational wave detectors like LIGO and Virgo have brought significant attention to binary systems composed of black holes and neutron stars as gravitational wave sources. However, two white dwarfs in a binary system are expected to be far more numerous. In particular, the pre-merger phase of double white dwarfs could lead to high-energy astrophysical events that would emit gravitational waves detectable by the European Space Agency’s upcoming Laser Interferometer Space Antenna (LISA) mission. Understanding how these double white dwarfs form is essential to interpreting the future LISA data. For the first time, researchers at the Max Planck Institute for Astrophysics (MPA) have now quantitatively assessed the impact of triple evolution on LISA sources. This study underscores the importance of triple interactions in the formation of double white dwarfs, revealing previously unexplored pathways that contribute to the gravitational-wave sources LISA will observe.

Stars often form in hierarchical triples, where a close binary system is orbited by a distant third star. These triple systems undergo complex gravitational interactions, which can dramatically alter the evolution of the stars. Such interactions can induce mass exchange between stars, mergers, or the disruption of one of the stars, all of which influence the final configuration of the system. Thus, triple dynamics can play a pivotal role in driving white dwarf binaries into the gravitational wave frequency range detectable by LISA.

In this research, doctoral student Abinaya Swaruba Rajamuthukumar, along with a group of MPA researchers, studied how triple star systems contribute to the population of double white dwarfs detectable by LISA. They combined simulations of triple star evolution using the Multiple Stellar Evolution (MSE) code with a Milky Way-like galaxy from the cosmological simulation TNG50. The study found that approximately 7.2 million double white dwarfs emitting gravitational waves in the LISA frequency band originate from triple systems, nearly double the number formed in isolated binaries, which account for about 3.8 million. Moreover, about 57% of the LISA double white dwarfs from triples retain a bound third star, though it is typically too distant to leave an observable imprint on the gravitational wave signal.

The team identified five key evolutionary pathways through which triple systems can produce LISA-detectable sources. These include induced mass transfer, outer binary mergers, ejected tertiaries, triple common envelope phases, and effectively isolated inner binaries (see graphic). The overall population properties of double white dwarfs from triple systems and those with a binary-origin are largely indistinguishable. Interestingly, the triple channel introduces a rare but intriguing subset of highly eccentric systems that emit burst-like gravitational wave signals, offering a distinct observational signature for LISA.

This study provides the first detailed exploration of triple-star evolution in the context of gravitational wave astrophysics. As LISA prepares for launch in 2035, these findings will be essential for accurately interpreting the Galactic population of gravitational wave sources and refining data analysis techniques. The results underscore the need to account for triple evolution when modeling LISA sources, paving the way for a more comprehensive understanding of the Milky Way’s gravitational wave sources.

Source: Max Planck Institute for Astrophysics/News

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Authors:

Abinaya Swaruba Rajamuthukumar
PhD student
tel:2248
abinaya@mpa-garching.mpg.de

Valeriya Korol
Postdoc
tel:2252
korol@mpa-garching.mpg.de

Jakob Stegmann
tel:2237
stegmaja@mpa-garching.mpg.de

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Original publication

Rajamuthukumar, Abinaya Swaruba; Korol, Valeriya; Stegmann, Jakob; Preece, Holly; Pakmor, Rüdiger; Justham, Stephen; Toonen, Silvia; de Mink, Selma E.
The role of triple evolution in the formation of LISA double white dwarfs
submitted Source

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A Universe made of Black Holes?

Fig. 3: Overall intensity of the gravitational-wave background generated by merging primordial black holes in the simulation, plotted as a function of time via the cosmological scale factor. LIGO/Virgo/Kagra limits today (scale factor 1 or redshift 0) are at the level of 10−7, about a factor 30 below the lower limit of the plot. © MPA

Video 1: Snapshot through the simulated region at different times during its evolution, showing the dark matter density. The left panel shows the case of particle dark matter, while the right panel shows the primordial-black-hole scenario. The middle panel illustrates the result if one were to approximate the evolution of primordial black holes by neglecting the small-scale binary interactions.

The nature of dark matter is still very much unknown; viable candidates range from microsopic elementary particles to black holes with masses many times that of the Sun. Researchers at MPA, Carnegie Observatories, and the University of Sussex have recently made concrete and reliable predictions for how the Universe would look if dark matter consists entirely of massive black holes: they performed the first self-consistent study of how structure would form in such a Universe, and how many of these black holes merge and emit observable gravitational waves.

Astronomers and cosmologists have collected a wide range of evidence for the existence of dark matter, a clustering matter component that has so far only been observed via its gravitational effects. Many dark matter candidates have been proposed, from microsopic elementary particles all the way to black holes with masses several times that of the Sun. Black holes comprising the dark matter would have to have formed in the early Universe, and hence are known as primordial black holes (PBH); astrophysically formed black holes (e.g., from stellar collapse) could not explain the evidence for dark matter seen in early-Universe probes, such as the cosmic microwave background, and would not be abundant enough. One possibility is that the PBHs were generated toward the end of the epoch of inflation in the early Universe.

A wide range of observations, including gamma-ray and X-ray backgrounds, gravitational lensing, the large-scale structure of the Universe, and the cosmic microwave background, have placed various constraints on the allowed PBH masses. Nevertheless, at least a fraction of dark matter might still consist of PBHs in several potential “mass windows”.

Researchers at MPA, Carnegie Observatories, and the University of Sussex have recently performed the first self-consistent study of how structure would form in a Universe with primordial-black-hole dark matter (of mass about 16 solar masses), by investigating the evolution of a region in the Universe with slightly above-average density. They carefully treated the evolution throughout the primordial Universe, and then continued the calculation with the state-of-the-art N-body code BIFROST. BIFROST calculates all gravitational forces between each black hole in the simulation without any small-scale resolution limit. It also includes relativistic effects responsible for libration and precession of binary PBH orbits, reminiscent of Einstein’s famous explanation for the periapsis advance of Mercury’s orbit. Most importantly, gravitational-wave radiation reaction effects are also modelled, allowing PBH binaries to merge in the simulations. This pilot study assumed that 100% of dark matter consists of PBHs. Mixed models with various dark matter components including collisional PBHs are numerically far more challenging to simulate, but might become feasible in the next few years.

The right column of Video 1 shows the evolution of the dark matter density in this scenario. For comparison, the team also performed simulations of the same region within a scenario where dark matter is made of microscopic particles (left column). The distribution of particle dark matter is much more smooth, while the discrete massive bodies are visible in the PBH simulation. The middle column shows the result of an approximate PBH simulation, where small-scale gravitational interactions are neglected; the clearly visible differences with the right column illustrate the importance of an accurate code like BIFROST for this study.

The dynamics of the system of black holes is highly complex. Close encounters between multiple black holes can lead to slingshot effects where one black hole is “kicked” with high velocity (the energy for this kick comes from the deep potential wells of the black holes). This is illustrated in Video 2, which shows the motions of individual black holes in the simulation over a short period of time (essentially, a dynamic, zoomed-in version of Video 1). Capturing these dynamics accurately while also being able to follow the system over the Universe’s history (or at least a substantial fraction of it) is very challenging, and this study presents the first such calculation ever performed.

Video 2: Motion of primordial black holes within a zoomed-in region over a short period of time. Multiple strong (“collisional”) dynamical effects are visible. Note that the PBH motion is interpolated for this video from the simulation output.

Given the dramatic differences between the primordial-black-hole and particle-dark-matter scenarios in Video 1, one would expect that astronomers could easily tell which scenario corresponds to the real Universe. However, we cannot observe either particle dark matter or black holes directly; moreover, the scales shown here are very small and difficult to probe. Thus, a bit of creativity is required to come up with observational routes to probe primordial black holes. For example, the “grainy” mass distribution in the primordial-black-hole case can affect (“heat”) the distribution of stars in galaxies.

One of the cleanest, and probably the most exciting probe of this scenario however are the gravitational waves emitted by the black hole population, in particular when two black holes merge, which happens when they get sufficiently close to each other. This is the subject of ongoing followup work by the team. A first result was already published in the study reported on here, however: the total intensity of all gravitational waves generated by mergers, as a function of time (Fig. 3). This signal is already several orders of magnitude larger than that observed in today’s Universe by the LIGO/Virgo/Kagra experiments, and is expected to put tough constraints on primordial black holes.

Moreover, the simulations predict that mergers of primordial black holes should already happen in the very young Universe (redshifts 𝑧>100), at a time before any stars have formed. Such a merger could not be explained by astrophysical black holes, and it would be a smoking-gun signal of primordial black holes. Future experiments such as the Einstein Telescope will actually be able to detect such mergers, if primordial black holes in the solar-mass range exist.

Source: Max Planck Institute for Astrophysics/News

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Antti Rantala
Postdoc
Tel: 2253
anttiran@mpa-garching.mpg.de

Fabian Schmidt
Scientific Staff
Member of the works council, Representative of the Scientific Coworkers
Tel: 2274
fschmidt@mpa-garching.mpg.de

Sten Delos
Carnegie Observatories
Research website

Sam Young
University of Sussex

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Original publication

M. Sten Delos, Antti Rantala, Sam Young, Fabian Schmidt

Structure formation with primordial black holes: collisional dynamics, binaries, and gravitational waves
JCAP12 (2024) 005

Source | DOI

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How stars stay young and spin slowly

Growth of density (top row) and magnetic field strength (bottom row) as a function of time in the collision between two stars of 0.7 and 0.6 solar masses. After the first contact at t = 0 h (not shown), the two stars pass each other (t = 5 h) and get disrupted (t = 12 h). The magnetic fields begin to grow due to instabilities and compression.© MPA

Computer simulations suggest that the amplification of magnetic fields in stellar collisions may play an important role in the formation of a particular subset of stars in clusters. Blue straggler stars in clusters appear not only bluer, but also younger than other cluster members. One proposed explanation for their apparently different ages is that they are the result of stellar collisions. However, this would require the resulting star to spin down efficiently without losing too much mass. Scientists at the Max Planck Institute for Astrophysics have now shown, using sophisticated 3D simulations, that the energy of the magnetic field is greatly amplified in the collisions of low-mass stars, providing a potentially efficient spin-down mechanism.

Clusters of stars, containing hundreds of thousands of stars that formed around the same time and from the same molecular cloud, provide astronomers with an excellent laboratory for studying how stars of similar age, composition and mass evolve over time. However, one particular subset, the 'blue stragglers', pose a challenge: they appear bluer and brighter than the other cluster members, and therefore appear to be younger. Why don't they age like typical cluster stars?

The answer could be that they actually formed later than the other stars in stellar collisions and thus gained mass. However, since most collisions between two low-mass stars are off-axis (rather than perfectly head-on), the resulting massive star would rotate rapidly and lose most of its mass during the spin-down to a stable state – unless the spin-down is efficient. While many proposed spin-down mechanisms require magnetic fields, it has remained unclear for more than two decades whether they actually exist and whether they have the strength to play a significant role.

A team at the Max Planck Institute for Astrophysics (MPA) has now presented sophisticated 3D moving-mesh magnetohydrodynamical simulations of collisions between low-mass main-sequence stars, which show that the magnetic field energy is amplified by a factor of up to 10 billion during collisions. At the core of the merged star, the magnetic field can reach 100 million Gauss (for comparison, the magnetic field in sunspots can reach up to 5000 Gauss). "Our simulations showed that the magnetic field in stellar collisions can be amplified, which is a promising sign for an effective spin-down mechanism," says MPA postdoctoral researcher Taeho Ryu, who led the study. "This amplification is independent of collision parameters, so it could happen every time two stars collide in a cluster."

The simulations also show a flattened, rotating gas structure around the collision, which could indicate the formation of a disk. Magnetic braking and an effect called "disk locking" could further facilitate the spin-down. "Our next step will be to actually follow the long-term evolution after the collision to see how these stars evolve over millions or billions of years and whether they really end up as the blue straggler stars that we observe," adds Ryu.

Magnetic field amplification in the collision of two low-mass stars

This animation shows the same simulation as the figure above. The left panel shows the evolution of the density, the right panel the evolution of the magnetic field strength as two stars of 0.7 and 0.6 solar masses collide.

Source: Max Planck Institute for Astrophysics

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Contact:

Taeho Ryu
Postdoc
2358
tryu@mpa-garching.mpg.de

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Original publication

Ryu, Taeho; Sills, Alison; Pakmor, Ruediger; de Mink, Selma; Mathieu, Robert
Magnetic Field Amplification during Stellar Collisions between Low-mass Stars
ApJ, Volume 980, Issue 2, id.L38, 11 pp.

Source | DOI

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A New Cosmic Ruler: Measuring the Hubble Constant with Type II Supernovae

Figure 1: Type II supernova sample used for the Hubble constant measurement. The images show the host galaxies of the ten supernovae, with the explosion sites marked by red star symbols. The images are aligned with a redshift scale reflecting the relative distances of the supernovae from Earth. © MPA

Figure 2: Spectral fitting and the Hubble diagram for Type II supernovae. The top panels show two examples of spectral fits used to determine the supernova distances. By comparing observed spectra (black) with model predictions (colour), researchers can extract key physical properties and infer the intrinsic brightness, enabling a direct distance measurement. The bottom panel presents a Hubble diagram, where the measured luminosity distances of the supernovae are plotted against their redshifts. The data points represent individual spectral observations, meaning multiple measurements can exist for each supernova. The dashed black line represents the best-fit relationship between distance and redshift, and its slope is determined by the Hubble constant. The grey-shaded regions indicate the uncertainties for this fit (68% and 95% confidence intervals). The best-fit value for the Hubble constant and its 68% confidence interval are H₀ = 74.9 ± 1.9 km/s/Mpc. © MPA

Figure 3: Artist’s impression of the Hubble tension, showing the two different approaches to measuring the Hubble constant as two bridges that do not quite connect. The depicted early-Universe measurements yield an average value of 67.4 km/s/Mpc, the local measurements an average value of 73.0 km/s/Mpc. The new measurement from this study, based on Type II supernovae (orange), is completely independent of all other measurements and provides compelling support for the Hubble tension. The local route also includes results from various incarnations of the cosmic distance ladder, as well as other direct methods such as gravitational lensing and water masers. Image Credit: Original image by NOIRLab/NSF/AURA/J. da Silva, sourced from NOIRLab (CC BY 4.0), modified by S. Taubenberger.

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The expansion rate of the Universe, quantified by the Hubble constant (H₀), remains one of the most debated quantities in cosmology. Measurements based on nearby objects yield a higher value than those inferred from observations of the early Universe—a discrepancy known as the "Hubble tension". Researchers at the Max Planck Institute for Astrophysics and their collaborators have now presented a new, independent determination of H₀ using Type II supernovae. By modeling the light from these exploding stars with advanced radiation transport techniques, they were able to directly measure distances without relying on the traditional distance ladder. The resulting H₀ value agrees with other local measurements and adds to the growing body of evidence for the Hubble tension, offering an important cross-check and a promising path toward resolving this cosmic puzzle.

One of the biggest puzzles in modern cosmology is the ongoing discrepancy in measurements of the Hubble constant (H₀) between local and early Universe probes, known as the “Hubble tension”. Since H₀ describes the current expansion rate of the Universe, it is a local quantity and can only be directly measured using nearby objects. In contrast, methods based on the early Universe, such as those using the cosmic microwave background (CMB), do not measure H₀ directly. Instead, they infer its value by assuming a cosmological model to extrapolate from the conditions 13 billion years ago to today. The fact that these two approaches yield conflicting values—with local distance-ladder measurements giving a higher H₀ than early-Universe methods—suggests that our standard cosmological model may be incomplete, potentially pointing to new physics.

Researchers at the Max Planck Institute for Astrophysics (MPA) and their collaborators have explored an independent way of measuring H₀ using Type II supernovae (SNe II). Unlike traditional approaches, this method does not rely on the cosmic distance ladder, making it a powerful cross-check against existing techniques. Their results provide a new, highly precise measurement of H₀ and further contribute to the debate over the expansion rate of the Universe.

Determining the Hubble constant requires accurate measurements of distances to astronomical objects at different redshifts. The most widely used technique, the cosmic distance ladder, relies on several interconnected steps: distances to nearby objects (such as Cepheid variable stars) are used to calibrate further reaching indicators such as Type Ia supernovae (SNe Ia), which then serve as standard candles to measure distances to faraway galaxies.

However, the reliance on multiple steps introduces possible systematic uncertainties, and different teams report slightly different results. A direct measurement based on known physics offers a valuable complementary approach, as it is affected by different systematics and does not depend on empirical calibrations. This is where Type II supernovae provide an exciting alternative.

Type II supernovae occur when massive, hydrogen-rich stars explode at the end of their lives. While their brightness varies depending on factors such as temperature, expansion velocity, and chemical composition, it can be accurately predicted using radiation transport models. This allows researchers to determine their intrinsic luminosity and use them as distance indicators, independent of empirical calibration methods.

A critical step in this process is identifying the best-fitting model for each observed supernova. Key physical properties leave distinct imprints on the supernova spectrum: temperature shapes the overall continuum, expansion velocity sets the width of spectral lines via Doppler broadening, and chemical composition determines the strength of specific absorption and emission features. By systematically comparing observed spectra to simulated spectra from radiative transfer models, researchers can find the model that most accurately describes the supernova’s physical conditions. With such a well-matched model the intrinsic brightness—and thus the distance—can be precisely determined.

To make this process efficient, the team used a spectral emulator, an advanced machine-learning tool trained on precomputed simulations. Instead of running time-intensive radiation transport calculations for every supernova, the emulator rapidly interpolates between models, allowing for fast and accurate spectral fitting.

The research team applied their spectral modeling approach to a sample of ten Type II supernovae at redshifts between 0.01 and 0.04, using publicly available data not specifically designed for distance measurements (Fig. 1). Despite the limitations of the dataset, their method yielded reliable distances. By constructing a Hubble diagram from these measurements (Fig. 2), they obtained an independent estimate of H₀: H₀ = 74.9 ± 1.9 km/s/Mpc

This value is consistent with most other local measurements, such as those from Cepheid-calibrated supernovae and supports the tension with early-Universe probes. The achieved precision is comparable to the most competitive techniques, demonstrating that Type II supernovae are a promising tool for cosmology (Fig. 3).

This study serves as a proof of concept, showing that Type II supernovae can provide precise and reliable distance measurements in the Hubble flow. Future work will focus on increasing the sample size and improving the accuracy of the technique by using dedicated observations. To this end, the researchers have assembled the adH0cc dataset (https://adh0cc.github.io/), a collection of Type II supernova observations from the ESO Very Large Telescope, specifically designed for precise distance measurements. This dataset will serve as a key resource for refining the method. By providing an independent check on the local determination of H₀, Type II supernovae help astrophysicists tackle one of the most pressing questions in cosmology today: Is the Hubble tension real, and if so, what does it tell us about the fundamental nature of the Universe?

Source: Max Planck Institute for Astrophysics/Research Highlights

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Authors:

Christian Vogl
Postdoc
2297
cvogl@mpa-garching.mpg.de

Stefan Taubenberger
2019
tauben@mpa-garching.mpg.de

Wolfgang Hillebrandt
Emeritus Director

Original publication

Vogl, Christian; Taubenberger, Stefan; et al.
No rungs attached: A distance-ladder free determination of the Hubble constant through type II supernova spectral modelling
submitted to A&A

Source

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Simulating the birth, life and dispersal of galactic star clusters

This illustration shows the galactic orbit (grey dots) of a star cluster (with 800 solar masses) that formed in a dwarf galaxy. The insets show individual cluster stars at three different times in the life-cycle of the star cluster: when the compact cluster has formed (red); after 50 Myr (half an orbit, green); and after 450 Myr (several orbits, blue), when the cluster is almost entirely disrupted. The background shows stars which have formed in the last 500 Myr (see movie below for details). © MPA

Most stars form in clusters, deeply embedded in the densest and coldest cores of giant molecular gas clouds. A few million years into the formation of a cluster the remaining gas is finally expelled by supernova explosions. Thereafter the clusters lose stars in the galactic tidal field and eventually disrupt. This entire life-cycle is very difficult to observe. Star clusters begin their lives deeply embedded in their birth clouds and are invisible to most observatories and the disruption of a single cluster can take tens of millions of years or more. An international team led by researchers at MPA has presented a new high-resolution supercomputer simulation, which can follow entire galactic star cluster life-cycles from birth to disruption and sheds light on the unobservable phases of star cluster evolution.

The complex life of star clusters

A typical young star cluster is a home to up to thousands of stars contained in a compact size of a few parsecs. The most massive ones, such as globular clusters, can exceed millions in their stellar count. Some of stars in these clusters are born with masses that exceed the mass of the Sun by tens or hundreds of times. Such massive stars are extremely rare (less than one in every 100 stars) and they live only for a few million years. They are, however, vitally important for creating new chemical elements through nuclear fusion, including those that are requisites for the formation of planets and the development of life.

Once massive stars form, they start releasing energetic photons and fast stellar winds that interact with the surrounding birth-cloud of gas. After a few million years, once the stars have exhausted their nuclear fuel, the most massive ones end their lives as explosive supernovae. These so called “feedback” processes deposit heat, momentum and heavy elements into the birth-cloud, eventually expelling the remaining gas that is left over from star formation.

This marks the transition of a young star cluster into a system that mainly evolves by gravitational interactions among its stars and with the surrounding tidal field. Through dynamical interactions, massive stars can sink to the centre of the cluster and stars can end up in binaries. Further gravitational interactions at the centre of the cluster force low mass stars on increasingly distant orbits. These stars can then become unbound and escape from the gravitational potential of the cluster into the galactic field. While orbiting in the host galaxy, the cluster continuously loses mass and ultimately disrupts entirely (Fig. 1).

More realistic star cluster simulations

Numerical simulations are an invaluable tool to probe the entire cycle of formation and disruption of star clusters on spatial and temporal scales that are inaccessible to observations (see previous Research Highlight December 2021 and Research Highlight October 2019). A recent study led by Postdoctoral Fellow Natalia Lahén at MPA presentedthe first star-by-star hydrodynamical galaxy simulations. Detailed modelling of individual stars is crucial for resolving the internal structure of star clusters. The simulation code for this project was first developed at MPA and further improved in international collaboration including researches at the University of Helsinki in Finland and Nicolaus Copernicus University in Poland. For the study presented here the team used a very accurate gravity solver to follow close gravitational interactions between stars. With this method it was possible to simulate, for the first time, the evolution of an entire dwarf galaxy with all its stars, gas and dark matter. At the same time, they could accurately follow the dynamical evolution of hundreds of individual star clusters, each containing at least hundreds or thousands of stars.

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Star cluster simulation

This movie follows the evolution of a low-mass galaxy for 500 million years modelled with the new method. The panels show the surface densities of stars (top left) and interstellar gas (top right), as well as the temperature (bottom left) and thermal pressure (bottom right) of the gas. Star clusters can be seen as concentrations of stellar mass, and the leading and trailing tidal tails extending from the clusters indicate that they are losing stars and being gradually disrupted. Energetic feedback from young massive stars can be seen as bubbles and cavities in the gas distribution.

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This figure shows the time evolution of the size and mass of a number of selected star clusters in the simulation. The color scale indicates the mean stellar age of the clusters and the black lines connecting the data points indicate the evolution of indiviual clusters. The clusters start embedded (triangles). They first contract and then expand once the star formation is halted and gas is removed (circles). The size evolution is compared to observed clusters in the Large and Small Magellanic clouds (green stars and crosses) and clusters in low-mass galaxies measured in the LEGUS galaxy survey (blue symbols). Even though the simulated clusters form very compact, they evolve to the observed range of sizes over ~10 million years. © MPA

Star cluster evolution in a galactic context

The new high-resolution simulations of a dwarf galaxy similar to Wolf–Lundmark–Melotte (WLM) in the Local Group (see the Movie for an illustration) show how gas and stars interact through cooling, collapse, star formation, and stellar feedback. The orbits as well as the release of energy and chemically enriched material of each star are followed individually along the stellar lifetime. Thanks to the new algorithm for gravitational force computation, in particular encounters with massive stars can be followed down to stellar radii and the dynamical evolution of the clusters embedded in the galactic interstellar medium can be followed at unprecedented accuracy.

The new simulations show that initially, while they are still embedded in the birth-cloud, star clusters can form very compact (see Figs. 1 and 2). During the following ten million years their sizes increase to the observed ~1 parsec due to dynamical evolution and stellar mass loss. The new methodology and its future expansion will play a key role in the next generation of simulations that aim to probe more extreme star forming systems called starbursts. Starbursts can be induced for example by compression of gas in galactic mergers or through gaseous inflows during the early cosmic epochs when galaxies themselves were still forming. The extreme gas densities promote the formation of increasingly massive star clusters.

The next step is to use the new methods to decipher the internal chemical and kinematic structure of the most massive clusters known as globular clusters. Globular clusters are the oldest bound star clusters observed in the Milky Way, dating back to the Cosmic Dawn. Understanding their birth conditions in synergy with state-of-the art observations of high-redshift star formation (from e.g. HST and JWST) as well as the Milky Way clusters (e.g. from Gaia and the upcoming 4MOST) may thus reveal how our home galaxy first started to form.

This work was supported by Gauss Centre for Supercomputing grants pn49qi and pn72bu at the GCS Supercomputer SUPERMUC-NG at Leibniz Supercomputing Centre and the Max Planck Computing and Data Facility.

Source: Max Planck Institute for Astrophysics/_Research Highlights

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Authors:

Natalia Lahén
Postdoc
tel: 2253
nlahen@mpa-garching.mpg.de

Antti Rantala
Postdoc
tel: 2253
anttiran@mpa-garching.mpg.de

Naab, Thorsten Naab
Scientific Staff
tel: 2295
tnaab@mpa-garching.mpg.de

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Original publications

1. Natalia Lahén, Antti Rantala, Thorsten Naab, Christian Partmann, Peter H. Johansson andJessica May Hislop

The formation, evolution and disruption of star clusters with improved gravitational dynamics in simulated dwarf galaxies

Monthly Notices of the Royal Astronomical Society, 2025

DOI

2. Natalia Lahén, Thorsten Naab, Guinevere Kauffmann, Dorottya Szécsi, Jessica May Hislop, Antti Rantala, Alexandra Kozyreva, Stefanie Walch and Chia-Yu Hu

Formation of star clusters and enrichment by massive stars in simulations of low-metallicity galaxies with a fully sampled initial stellar mass function

Monthly Notices of the Royal Astronomical Society, 2023, Volume 522, Issue 2, pp.3092-3116

Source

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Debugging Galaxy Evolution with L-GALAXIES

The semi-analytical model L-GALAXIES simulates astrophysical phenomena to predict galaxy properties and scaling relations. Composite image: MPA

The three plots show the L-GALAXIES model predictions (solid lines) for Milky Way-mass galaxies compared to observational data points at the corresponding redshift. The left plot demonstrates that the model fails to produce a sufficient number of quenched galaxies. The middle plot indicates that the model overestimates the sizes of quenched galaxies. The plot on the right shows that quenched galaxies in the model are not sufficiently compact. © MPA

The plot illustrates the gas fractions within galaxy halos as a function of halo mass for six redshift intervals (various colors) from two simulations (dashed and solid lines). The lack of redshift evolution suggests that the physical processes governing gas retention within halos in the L-GALAXIES model are largely time-independent. The AGN feedback in L-GALAXIES primarily prevents hot gas cooling without significantly altering its spatial distribution. © MPA

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The formation and evolution of galaxies are among the most complex challenges in astrophysics. Recent advancements with instruments like JWST and ALMA have shed light on high-redshift galaxies – those that existed billions of years ago. However, most theoretical models are tuned to match galaxies in the local universe. Researchers from the Max Planck Institute for Astrophysics and the University of Bonn now comprehensively evaluated the Munich semi-analytical model L-GALAXIES using the latest observations and found that while the model aligns well with the properties of local galaxies, it struggles with key aspects of high-redshift galaxies. Particularly, the study highlights critical issues with the model’s predictions of quenched galaxies, those that have ceased star formation. Their results suggest a need to revise the implementation of processes driving star formation quenching, including supermassive black hole feedback and galaxy mergers.

Observations from surveys such as SDSS, CANDELS, and COSMOS provide essential insights into galaxy properties and scaling relations. However, to uncover the underlying processes driving galaxy evolution, astronomers need to simulate the relevant astrophysical phenomena. The Munich semi-analytical model, L-GALAXIES, offers a self-consistent framework for tackling these challenges. Over the past three decades, L-GALAXIES has undergone continuous development, primarily at the Max Planck Institute for Astrophysics (MPA) in collaboration with international teams, establishing itself as a corner-stone tool for studying galaxy evolution. The model strikes a balance between computational efficiency and detailed physical modelling, making it a powerful complement to computationally demanding hydro-dynamical simulations.

The L-GALAXIES model builds upon its previous generation with a series of advancements that are motivated both by new observational data and a resulting deeper physical understanding of complex processes such as gas accretion and cooling, star formation, chemical enrichment, and stellar and black hole feedback. The most recent versions incorporate advanced environmental mechanisms like ram-pressure and tidal stripping. The models are calibrated using Monte Carlo Markov Chain (MCMC) techniques and constrained by low-redshift observational data. Together, these updates and calibrations represent the cutting edge of semi-analytical galaxy formation modelling.

Recent observational campaigns, particularly those utilizing advanced ground- and space-based instruments such as the Hubble Space Telescope (HST), the Atacama Large Millimeter/submillimeter Array (ALMA), and the James Webb Space Telescope (JWST), have provided unprecedented insights into the evolution of high-redshift galaxies. These observations reveal the size, compactness, and abundance of quenched galaxies at redshifts around z=2 (when the universe was just 3 billion years old) and beyond, offering a unique opportunity to rigorously test L-GALAXIES predictions well outside its original calibration regime. In particular, they are identifying areas where the model aligns with or deviates from observed trends, providing crucial guidance for improving its treatment of high-redshift galaxy populations.

The current study evaluates the latest version of L-GALAXIES alongside its two preceding iterations, focusing on their ability to reproduce the evolution of galaxy number density, size, and surface density across cosmic time. The analysis spans the history of the universe, from 500 million years after the Big Bang to the present day (~13.5 billion years later), with a specific focus on the first few billion years. It marks the first comprehensive comparison of L-GALAXIES predictions to high-redshift observations.

Galaxies were classified as star-forming or quenched based on their near-ultraviolet (NUV) to near-infrared (J-band) color. Sizes and surface densities were determined using methodologies consistent with observational studies. Additionally, X-ray data from instruments such as Chandra and XMM-Newton, along with microwave and longer wavelength data from Planck, were incorporated to examine baryon and gas distributions within host halos, shedding light on the interaction between baryonic matter and galaxy processes.

Although the model shows significant agreement with the properties of star-forming galaxies at both low and high redshifts, the study highlights significant discrepancies in the model’s predictions for quenched galaxies, particularly for Milky Way-mass and more massive systems at the times when the Universe was younger than 2 billion years old. The model underestimates the abundance of quenched galaxies by a factor of 60 and over-predicts the fraction of baryonic matter within galaxy clusters by around 15-20%. Moreover, the predicted sizes of galaxies are several times larger than observed, pointing to deficiencies in the modelling of star formation suppression mechanisms such as active galactic nucleus (AGN) feedback and galaxy mergers.

Source: Max Planck Institute for Astrophysics/Research Highlights

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Author:

Akash Vani
tel:2298
vani@mpa-garching.mpg.de

Original publication

Akash Vani, Mohammadreza Ayromlou, Guinevere Kauffmann, Volker Springel
Probing galaxy evolution from z = 0 to z ≃ 10 through galaxy scaling relations in three L-GALAXIES flavours
Monthly Notices of the Royal Astronomical Society, Volume 536, Issue 1, January 2025, Pages 777–806

Source | DOI

More Information

LGalaxies website

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Researchers capture direct high-definition image of the “Cosmic Web”

Simulation of a vast region of the Universe based on the current cosmological model and performed using supercomputers. In the image, the faint glow of the gas within the cosmic filaments, forming a dense cosmic web, is shown in white. At the intersections of these filaments, the gas within galaxies, which fuels the formation of new stars, is highlighted in red. © Alejandro Benitez-Llambay/Universität Mailand-Bicocca/MPA

The image shows the diffuse gas (yellow to purple) contained within the cosmic filament connecting two galaxies (yellow stars), extending across a vast distance of 3 million light-years. © Davide Tornotti/University of Milano-Bicocca

A twin of the cosmic filament observed in the MUDF as seen in a supercomputer simulation describing the large-scale distribution of gas in the Universe. The gas flowing within the cosmic web, feeding galaxy formation at filament intersections, is shown in purple. Davide Tornotti/University of Milano-Bicocca/MPA

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Matter in intergalactic space is distributed in a vast network of interconnected filamentary structures, collectively referred to as the cosmic web. With hundreds of hours of observations, an international team of researchers has now obtained an unprecedented high-definition image of a cosmic filament inside this web, connecting two active forming galaxies – dating back to when the Universe was about 2 billion years old.

A pillar of modern cosmology is the existence of dark matter, which constitutes about 85% of all matter in the Universe. Under the influence of gravity, dark matter forms an intricate cosmic web composed of filaments, at whose intersections the brightest galaxies emerge. This cosmic web acts as the scaffolding on which all visible structures in the Universe are built: within the filaments, gas flows to fuel star formation in galaxies. Direct observations of the fuel supply of such galaxies would advance our understanding of galaxy formation and evolution

. However, studying the gas within this cosmic web is incredibly challenging. Intergalactic gas has been detected mainly indirectly through its absorption of light from bright background sources. But the observed results do not elucidate the distribution of this gas. Even the most abundant element, hydrogen, emits only a faint glow, making it basically impossible for instruments of the previous generation to directly observe such gas.

In this new study, an international team led by researchers at the University of Milano-Bicocca and including scientists at the Max Planck Institute for Astrophysics (MPA) obtained an unprecedented high-definition image of a cosmic filament using MUSE (Multi-Unit Spectroscopic Explorer), an innovative spectrograph installed on the Very Large Telescope at the European Southern Observatory in Chile. Even with the advanced capabilities of this sophisticated instrument, the research group had to carry out one of the most ambitious MUSE observation campaigns ever completed in a single region of the sky, acquiring data over hundreds of hours to detect the filament at high significance.

The study, led by Davide Tornotti, PhD student at the University of Milano-Bicocca, used this ultrasensitive data to produce the sharpest image ever obtained of a cosmic filament spanning 3 million light-years and connecting two galaxies, each hosting an active supermassive black hole. The discovery, recently published in Nature Astronomy opens new avenues to directly constrain gas properties within intergalactic filaments and to refine our understanding of galaxy formation and evolution.

“By capturing the faint light emitted by this filament, which travelled for just under 12 billion years to reach Earth, we were able to precisely characterize its shape, explains Davide Tornotti. “For the first time, we could trace the boundary between the gas residing in galaxies and the material contained within the cosmic web through direct measurements.” The researchers took advantage of supercomputer simulations of the Universe run at MPA to calculate predictions of the expected filamentary emission given the current cosmological model. “When comparing to the novel high-definition image of the cosmic web, we find substantial agreement between current theory and observations,” Tornotti adds.

This discovery and the encouraging agreement with supercomputer simulations are key to understanding the tenuous gas environment around galaxies and open up novel possibilities to pin down the galaxies’ fuel supply. Fabrizio Arrigoni Battaia, MPA staff scientist involved in the study, concludes: “We are thrilled by this direct, high-definition observation of a cosmic filament. But as people say in Bavaria: ‘Eine ist keine’ – one doesn’t count. So we are gathering further data to uncover more such structures, with the ultimate goal to have a comprehensive vision of how gas is distributed and flows in the cosmic web.”

Source: Max Planck Institute for Astrophysics/Press Releases

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Contact:

Fabrizio Arrigoni Battaia
Scientific Staff
tel:2288
arrigoni@mpa-garching.mpg.de

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Original publication

Davide Tornotti et al.
High-definition imaging of a filamentary connection between a close quasar pair at z=
Nature Astronomy, 29 January 2025

Source

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More Information

Revealing a filament from the cosmic web
ESO Press Release

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Towards direct observation of large samples of intergalactic filaments in the early universe

One quasar of the sample embedded into extended Lyman alpha emission (cyan), which reaches the edge of the circumgalactic medium of its host galaxy. The uncovered filamentary structure is stretched in the direction of the second quasar of the pair (not shown). Multiple further sources are visible in this field, which are not physically associated with the quasar pair; these lie between Earth and the observed quasar. © MPA

This plot shows the alignment of the Lyman alpha nebulae with the quasar pair direction. An angle of zero degrees corresponds to perfect alignment. In the sample studied, all large nebulae (extending into the circumgalactic medium by more than 200,000 light years) trace the quasar pair direction. This trend is not driven by the quasar luminosity (colour of the points) or the distance between the quasar pairs (size of the dots). This shows that the Lyman alpha nebulae indeed trace the cosmic web filaments. © MPA

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The distribution of matter in the universe is predicted by supercomputer simulations to occur in a network of filaments, known as the "cosmic web", where galaxies form and evolve. The vast majority of this intricate structure is in the form of diffuse hydrogen gas, so rarefied that it is extremely challenging to observe it directly. A collaboration led by MPA researchers has targeted the active supermassive black holes of galaxy pairs at close separations to reveal the connecting filamentary structures of the cosmic web in the early universe. The results are promising and unveil evidence for such structures stretching between the observed pairs, ultimately providing excellent targets for future ultra-deep observations.

Galaxies are embedded in large reservoirs of gas bound to them by gravity, the so-called 'circumgalactic medium'. Like all gas in the universe, it mainly consists of hydrogen and helium with traces of other elements that are produced in stars and ejected from the galaxy disks in bubbles of hot gas or fast winds expanding into the circumgalactic medium. In turn, cool gas is funneled back into the galaxy in streams and can form new stars or feed the supermassive black hole at the galactic centre. Galaxies are not hermits though: large filamentary gas structures connect galaxies to their neighbours. This overall skeleton is called 'cosmic web' (see Monthly Highlight of June 2024), and galaxies can accrete additional material from its filaments to rejuvenate and grow. While simulations have explored this process very well, observational evidence of the filamentary cosmic web is sparse and mainly indirect, e.g. inferred from the observed position of galaxies in the local universe or by how the cosmic web absorbs light from bright background sources.

The areas where multiple filaments of the cosmic web intersect are called 'nodes', typically inhabited by the most massive galaxies. In the early universe, 11.5 billion years ago, these massive galaxies are commonly pinpointed by quasars – a brief phase in these galaxies’ life cycle, when matter falling onto their central supermassive black holes powers exceptionally luminous events that easily outshine all stars in their host galaxy. Therefore quasars can act as powerful natural 'cosmic flashlights': Their radiation can reach far into the circumgalactic medium and the surrounding cosmic web, lighting up the hydrogen gas at a specific ultraviolet colour, the Lyman alpha wavelength.

Researchers from MPA have now observed a sample of quasar pairs, i.e. two massive active galaxies in direct vicinity to each other, to unveil the Lyman alpha emission in their circumgalactic medium and in-between the galaxies (commonly referred to as 'Lyman alpha nebulae'). Extended emission is detected in most targeted systems (see example in Fig. 1) and the emission is preferentially aligned with the pair direction (see Fig. 2). These results are in line with expectations, if a cosmic web filament connects the two quasars and cool gas gets funneled directly from the filament through the circumgalactic medium down to the galactic disk.

Compared to other massive galaxies at this epoch, quasar pairs are embedded in smaller reservoirs of cool gas. Their circumgalactic medium actually resembles that of galaxies at a cosmic time one billion years later. Such an accelerated evolution might be caused by the rich environment inhabited by quasar pairs and/or by highly energetic processes connected to the accreting supermassive black holes, which could heat up the gas surrounding the galaxy and counteract the gas accretion.

This sample of quasar pair observations is the largest to date and represents the best collection of promising targets for directly studying the emission of the cosmic web in the early universe with future ultra-deep observations. More and more observations of the intricate web of cosmic filaments will become available in the near future.

Source: Max Planck Institute for Astrophysics/News

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Author:

Eileen Herwig
PhD student
tel:2344
eherwig@mpa-garching.mpg.de

Original publication

Eileen Herwig
Arrigoni Battaia, Fabrizio;
González Lobos, Jay; et al.
QSO MUSEUM: II. Search for extended Lyα emission around eight z ∼ 3 quasar pairs
A&A, 691, A210 (2024)

Source | DOI

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