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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How galaxies make black holes collide

Schematic overview of a wide binary orbiting inside the Milky Way. While moving through the Galaxy its ellipticity gets modulated by the gravity of the Galaxy and fly-bys from ambient stars, leading to close encounters (inset). Credit: Jakob Stegmann et al 2024 ApJL 972 L19

Illustration of two equal-mass objects moving around each other on a circular orbit (left panel) and more and more elliptical orbits (towards the right). While all objects remain widely separated for most of the time, those moving on a very elliptical trajectory encounter each other very closely once per orbit. Credit: A. Price-Whelan/Creative Commons CC-BY-SA licence

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The groundbreaking detections of gravitational waves from merging pairs of black holes have left us with an intriguing question: how do black holes get close enough to merge? Scientists at MPA show that some of them may have started out as massive stars orbiting one another at extremely large separations — 1,000 to 10,000 times the distance between Earth and Sun. Once these stars end their lives and form black holes, the gravity of the entire galaxy in which they reside could slowly deform the shape of their orbit leading to a close encounter and merger of the black holes.

A large fraction of stars are not alone. Observations show that, unlike our Sun, many of them are orbited by a stellar companion and form a so-called binary. The separation at which these binary stars orbit one another closely determines their evolution. On the one hand, stars on very tight orbits are prone to exchange mass leading to a complex interactive stellar evolution. For massive stars, these interactions may leave behind a close binary black hole which could eventually merge due to the energy-loss from gravitational-wave emission. On the other hand, binary stars at wider separations were previously thought to evolve rather unspectacularly, effectively as single stars, leaving behind binary black holes which are too far apart to merge.

In a recent study, published in the The Astrophysical Journal Letters, a group of researchers led by MPA research fellow Jakob Stegmann question this standard lore of binary physics and show that it is only true as long as the binaries are considered to be in isolation. In reality, they are embedded in a galactic environment in which wide binaries separated by more than 1,000 Earth-Sun distances are vulnerable to perturbations from the gravity of the host galaxy and from fly-bys of ambient stars. Taking into account this galactic influence, the study shows that the dynamics of wide binaries can give rise to extreme interactions between stars and compact remnants.

These interactions are a consequence of the extremely low binding energy that holds very wide binary black holes together. Thus, the gravitational pull of the entire host galaxy can slowly deform the shape of the orbit on which the two black holes move around each other and make it more and more elongated. On these highly elliptical orbits the two black holes remain widely separated for most of the time, but pass close to each other once per orbit (see animation). This leads to a counterintuitive result: In order to bring two black holes closer than a few kilometres so that they can merge, we could nevertheless start with a wide separation of more than 1,000 times the distance between Earth and Sun. The clue lies in the ellipticity of their orbit which slowly grows due to the disturbing effect of the galaxy’s gravity.

This mechanism of driving two black holes closer together could also be relevant for the evolution of wide low-mass binary stars. Recently, researchers at MPIA in Heidelberg have searched for wide binaries in the data from the ESA-led mission Gaia. Surprisingly, they found that about ten percent of all low-mass stars possess a distant stellar companion. While systems like those are not massive enough to develop black holes, in this case the MPA study shows that the gravity of the galaxy could drive the stars to a head-on collision. These collisions would not lead to detectable emission of gravitational waves, but could be visible as energetic flares, so-called Luminous Red Novae.

The results of this study represent progress in investigating the plethora of evolutionary pathways of binary stars and their compact remnants. While previous work on wide binaries has mostly focused on ruling out the existence of a distant companion to our Sun (referred to as the “Nemesis hypothesis”), on the one hand, and understanding the upper limit of their separation to remain bound, on the other hand, little attention has been paid to studying the interactions between wide binary stars. With future data releases of Gaia expanding the catalogue of wide binary stars at an unprecedented rate, the MPA study makes an important step towards understanding their co-evolution with the Milky Way. Investigating their dynamics in detail allows us to understand how systems previously thought uneventful could in fact lead to some of the most energetic transients in the Universe.

Source: Max Planck Institute for Astrophysics/News

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Author:

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

Original Publication

Jakob Stegmann, Alejandro Vigna-Gómez, Antti Rantala, Tom Wagg, Lorenz Zwick, Mathieu Renzo, Lieke A. C. van Son, Selma E. de Mink, and Simon D. M. White

Close Encounters of Wide Binaries Induced by the Galactic Tide: Implications for Stellar Mergers and Gravitational-wave Sources

https://iopscience.iop.org/article/10.3847/2041-8213/ad70bb

Source | DOI

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Gemini South Captures Cosmic ‘Cotton Candy’

PR Image noirlab2329a
Gemini South Reveals Tangled Spiral Arms of the Peculiar Galaxy NGC 7727

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Chaotic jumble of merging spiral galaxies hints at possible fate of Milky Way and Andromeda galaxies

Gemini South, one half of the International Gemini Observatory operated by NSF’s NOIRLab, captures the billion-year-old aftermath of a spiral galaxy collision. At the heart of this chaotic interaction, entwined and caught in the midst of the chaos, is a pair of supermassive black holes — the closest such pair ever recorded from Earth.

The swirling arms of a spiral galaxy are among the most recognized features in the cosmos: long sweeping bands spun off from a central core, each brimming with dust, gas, and dazzling pockets of newly formed stars. Yet this opulent figure can warp into a much more bizarre and amorphous shape during a merger with another galaxy. The same sweeping arms are suddenly perturbed into disarray, and two supermassive black holes at their respective centers become entangled in a tidal dance. This is the case of NGC 7727, a peculiar galaxy located in the constellation of Aquarius about 90 million light-years from the Milky Way.ever recorded from Earth.

Astronomers have captured an evocative image of this merger’s aftermath using the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini South telescope in Chile, part of the International Gemini Observatory operated by NSF’s NOIRLab. The image reveals vast swirling bands of interstellar dust and gas resembling freshly-spun cotton candy as they wrap around the merging cores of the progenitor galaxies. From the aftermath has emerged a scattered mix of active starburst regions and sedentary dust lanes encircling the system.ever recorded from Earth.

What is most noteworthy about NGC 7727 is undoubtedly its twin galactic nuclei, each of which houses a supermassive black hole, as confirmed by astronomers using the European Southern Observatory’s Very Large Telescope (VLT). Astronomers now surmise the galaxy originated as a pair of spiral galaxies that became embroiled in a celestial dance about one billion years ago. Stars and nebulae spilled out and were pulled back together at the mercy of the black holes’ gravitational tug-of-war until the irregular tangled knots we see here were created.

The two supermassive black holes, one measuring 154 million solar masses and the other 6.3 million solar masses, are approximately 1600 light-years apart [1]. It is estimated that the two will eventually merge into one in about 250 million years to form an even more massive black hole while dispersing violent ripples of gravitational waves across spacetime.

Because the galaxy is still reeling from the impact, most of the tendrils we see are ablaze with bright young stars and active stellar nurseries. In fact, about 23 objects found in this system are considered candidates for young globular clusters. These collections of stars often form in areas where star formation is higher than usual and are especially common in interacting galaxies as we see here.

Once the dust has settled, NGC 7727 is predicted to eventually become an elliptical galaxy composed of older stars and very little star formation. Similar to Messier 87, an elliptical galaxy with a supermassive black hole at its heart, this may be the fate of the Milky Way and the Andromeda Galaxy when they fuse together in billions of years’ time.

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More information

[1] The supermassive black hole at the center of the Milky Way contains a relatively modest 4.3 million solar masses. The most massive black hole observed to date contains approximately 66 billion solar masses.

NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory), the US center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

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Links

• Photos of the Gemini South telescope
• Videos of the Gemini South telescope

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Contacts

Josie Fenske
NSF’s NOIRLab Communications
Email: josie.fenske@noirlab.edu

Source: NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab)/News

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Gravitational Waves Shed Light on How Heavy a Neutron Star Can Be

This still comes from a simulation of two neutron stars merging. Observations of collisions like these may help us determine the maximum mass a neutron star can attain. Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla

Artist’s impression of a strongly magnetized neutron star.
Credit:NASA/Penn State University/Casey Reed

Probability distribution function for the maximum mass of a non-rotating neutron star, as estimated by the authors’ genetic algorithm (blue curve) and in a previous study of GW170817 (purple curve). Credit: Nathanail et al. 2021 

What’s the largest mass that a neutron star — the dense, collapsed core of a massive star — can grow to before further collapsing into a black hole? Recent gravitational-wave events are providing new insight.

Finding the Maximum

Neutron stars consist almost entirely of neutrons packed together at the density of atomic nuclei. This extreme mass in such a small space results in an extraordinary inward gravitational pull that increases as more neutrons are packed in. When the crushing gravitational force exceeds the combined quantum and nuclear forces pushing outward, the star collapses to form a black hole.

What is the maximum mass limit above which a neutron star collapses? Theory suggests that, for a non-rotating neutron star, it’s somewhere around 2 or 3 times the mass of the Sun — but the precise value relies on the unknown state of matter inside the neutron star. To get around this missing information, we need observational constraints to help us pin down how heavy a neutron star can be.

Collisional Clues

In recent years, gravitational waves have provided valuable new insight. Two particular mergers of compact objects have tempted us with clues:

1. GW170817
   
   In this event, two neutron stars in the range of 1.1–1.6 solar masses merged to form a larger object, which we think collapsed into a black hole shortly after merger. The gravitational-wave and electromagnetic observations of this process point to a maximum neutron star mass that’s less than 2.3 solar masses.
2. GW190814
   
   In this event, a black hole of more than 20 solar masses merged with an object of just 2.5–2.7 solar masses — but we don’t know whether that smaller object was a black hole or a neutron star. If it was a non-rotating neutron star, then this would imply that the upper limit for neutron star mass is above 2.5 solar masses.

Can we reconcile these two potentially conflicting pieces of information? A study led by Antonios Nathanail (Institute for Theoretical Physics, Germany) presents new analysis that further explores what these mergers tell us about neutron star limits.

Probability distribution function for the maximum mass of a non-rotating neutron star, as estimated by the authors’ genetic algorithm (blue curve) and in a previous study of GW170817 (purple curve). Credit: Nathanail et al. 2021

A Lower Upper Limit

Nathanail and collaborators analyzed these two mergers by employing a genetic algorithm — an algorithm that explores a large parameter space and looks for optimized solutions by mimicking the process of natural selection. Using this algorithm, the authors identified which maximum mass solutions are consistent with gravitational-wave and electromagnetic observations of GW170817 and GW190814 and numerical simulations of mergers.

From their systematic investigation, the authors show that a large maximum neutron star mass — like the 2.5 solar masses required if GW190814’s secondary was a non-rotating neutron star — doesn’t mesh with our observations of GW170817 or with expectations from numerical simulations of gravitational wave production.

Instead, the authors find that a maximum neutron star mass of about 2.2 solar masses neatly reproduces the observations of GW170817 and is consistent with numerical simulations. This upper limit implies that GW190814’s secondary was too large to have been a non-rotating neutron star. Instead, GW190814 was likely the merger of two unequal-mass black holes.

Citation

“GW170817 and GW190814: Tension on the Maximum Mass,” Antonios Nathanail et al 2021 ApJL 908 L28.doi:10.3847/2041-8213/abdfc6

By Susanna Kohler

 

 Source: American Astronomical Society (AAS NOVA)

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Primordial black holes and the search for dark matter from the multiverse

Fig1. Baby universes branching off of our universe shortly after the Big Bang appear to us as black holes.
Credit：Kavli IPMU

Fig2. Hyper Suprime-Cam (HSC) is a gigantic digital camera on the Subaru Telescope
Credit：HSC project / NAOJ

Fig3. The Subaru Telescope in Hawaii.
Credit：NAOJ

Fig4. A star in the Andromeda galaxy temporarily becomes brighter if a primordial black hole passes in front of the star, focusing its light in accordance with the theory of gravity. (Credit: Kavli IPMU/HSC Collaboration)

 

The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) is home to many interdisciplinary projects which benefit from the synergy of a wide range of expertise available at the institute. One such project is the study of black holes that could have formed in the early universe, before stars and galaxies were born.  

Such primordial black holes (PBHs) could account for all or part of dark matter, be responsible for some of the observed gravitational waves signals, and seed supermassive black holes found in the center of our Galaxy and other galaxies. They could also play a role in the synthesis of heavy elements when they collide with neutron stars and destroy them, releasing neutron-rich material. In particular, there is an exciting possibility that the mysterious dark matter, which accounts for most of the matter in the universe, is composed of primordial black holes. The 2020 Nobel Prize in physics was awarded to a theorist, Roger Penrose, and two astronomers, Reinhard Genzel and Andrea Ghez, for their discoveries that confirmed the existence of black holes. Since black holes are known to exist in nature, they make a very appealing candidate for dark matter. 

The recent progress in fundamental theory, astrophysics, and astronomical observations in search of PBHs has been made by an international team of particle physicists, cosmologists and astronomers, including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.

To learn more about primordial black holes, the research team looked at the early universe for clues. The early universe was so dense that any positive density fluctuation of more than 50 percent would create a black hole. However, cosmological perturbations that seeded galaxies are known to be much smaller. Nevertheless, a number of processes in the early universe could have created the right conditions for the black holes to form.  

One exciting possibility is that primordial black holes could form from the “baby universes” created during inflation, a period of rapid expansion that is believed to be responsible for seeding the structures we observe today, such as galaxies and clusters of galaxies. During inflation, baby universes can branch off of our universe. A small baby (or “daughter”) universe would eventually collapse, but the large amount of energy released in the small volume causes a black hole to form.  

An even more peculiar fate awaits a bigger baby universe. If it is bigger than some critical size, Einstein's theory of gravity allows the baby universe to exist in a state that appears different to an observer on the inside and the outside. An internal observer sees it as an expanding universe, while an outside observer (such as us) sees it as a black hole. In either case, the big and the small baby universes are seen by us as primordial black holes, which conceal the underlying structure of multiple universes behind their “event horizons.” The event horizon is a boundary below which everything, even light, is trapped and cannot escape the black hole. 

In their paper, the team described a novel scenario for PBH formation and showed that the black holes from the “multiverse” scenario can be found using the Hyper Suprime-Cam (HSC) of the 8.2m Subaru Telescope, a gigantic digital camera - - the management of which Kavli IPMU has played a crucial role - - near the 4,200 meter summit of Mt. Mauna Kea in Hawaii. Their work is an exciting extension of the HSC search of PBH that Masahiro Takada, a Principal Investigator at the Kavli IPMU, and his team are pursuing. The HSC team has recently reported leading constraints on the existence of PBHs in Niikura, Takada et. al. Nature Astronomy 3, 524–534 (2019)

Why was the HSC indispensable in this research? The HSC has a unique capability to image the entire Andromeda galaxy every few minutes. If a black hole passes through the line of sight to one of the stars, the black hole’s gravity bends the light rays and makes the star appear brighter than before for a short period of time. The duration of the star’s brightening tells the astronomers the mass of the black hole. With HSC observations, one can simultaneously observe one hundred million stars, casting a wide net for primordial black holes that may be crossing one of the lines of sight.  

The first HSC observations have already reported a very intriguing candidate event consistent with a PBH from the “multiverse,” with a black hole mass comparable to the mass of the Moon. Encouraged by this first sign, and guided by the new theoretical understanding, the team is conducting a new round of observations to extend the search and to provide a definitive test of whether PBHs from the multiverse scenario can account for all dark matter.  

Source: Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)

 

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Paper details

Journal: Physical Review Letters
Title: Exploring Primordial Black Holes from the Multiverse with Optical Telescopes
Authors: Alexander Kusenko (1, 2), Misao Sasaki (2, 3, 4), Sunao Sugiyama (2, 5), Masahiro Takada (2), Volodymyr Takhistov (1,2), and Edoardo Vitagliano (1)

Author affiliation: 

1. Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095-1547, USA 
2. Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
3. Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan 
4. Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 10617, Taiwan 
5. Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

DOI: https://doi.org/10.1103/PhysRevLett.125.181304  (October 30, 2020)
Abstract of the paper: (Physical Review Letters)
Preprint: (arXiv.org page)  

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Research contact:

Alexander Kusenko
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Visiting Senior Scientist
Department of Physics & Astronomy, University of California, Los Angeles
Professor
E-mail: kusenko@ucla.edu

Misao Sasaki
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Deputy Director
Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University
Leung Center for Cosmology and Particle Astrophysics, National Taiwan University
E-mail: misao.sasaki@ipmu.jp

Sunao Sugiyama
Graduate Student
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Department of Physics, The University of Tokyo
E-mail: sunao.sugiyama@ipmu.jp

Masahiro Takada
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Principal Investigator
E-mail: masahiro.takada@ipmu.jp

Volodymyr Takhistov
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Project Researcher / Kavli IPMU Fellow
E-mail: volodymyr.takhistov@ipmu.jp

Media contact:

John Amari
Press officer 
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
E-mail: press@ipmu.jp
TEL: 080-4056-2767 

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Signs of Collisions to Come

Artist’s impression of a neutron star threaded with a dipole magnetic field.
Credit:[ESO/L.Calçada]. Hi-res Image

Artist’s impression of the collision and merger of two neutron stars.
Credit:[NSF/LIGO/Sonoma State University/A. Simonnet]. Hi-res Image

We know that when two neutron stars — the dense, compact cores of evolved stars — collide, they produce signals that span the electromagnetic spectrum. But could these binaries also flare before they merge, as well?

A Broad Range of Signals

The discovery and follow-up of the gravitational-wave event GW170817, a collision of two neutron stars, provided the first direct evidence of the many forms of light that are emitted in these mergers. Between the instant of collision and the months that followed, observatories around the world recorded everything from high-energy gamma rays to late-time radio emission.

But emission might not be restricted to during and after the merger! A new study conducted by two researchers from the Flatiron Institute, Elias R. Most (also of Goethe University Frankfurt, Germany) and Alexander Philippov, explores the possibility that neutron star binaries may also produce flares of emission in the time leading up to their final impact.

This plot of the out-of-plane magnetic field density indicates the twist in flux tubes connecting the two neutron stars seen at the center of the plot. Here, an electromagnetic flare is launched from the binary after a significant twist has built up due to relative rotation of the right star. [Most & Philippov 2020]. Hi-res Image

What About Magnetic Fields?

In particular, Most and Philippov focus on how the magnetospheres of the two neutron stars — the magnetized environment surrounding each body — interact shortly before the objects collide.

The authors conduct special-relativistic force-free simulations of orbiting pairs of neutron stars in which each star is threaded with the strong dipole magnetic field expected for these bodies. The simulations then track how the stars’ magnetic fields evolve, twist, and interact as the bodies orbit each other.

A Twisted Fate

Most and Philippov find that dramatic releases of magnetic energy are a common outcome if the neutron stars orbit close enough to one another that their magnetospheres interact.

The authors show that the brightness of the flare luminosity depends only on how far apart the neutron stars are in the simulation: the smaller the separation, the brighter the flare. This dependence demonstrates that the flaring events are driven primarily by the energy stored in the twisted tube of magnetic flux that forms connecting the two neutron stars.

When the two neutron stars spin at different speeds, the magnetic field loop that forms between the stars becomes progressively more twisted — until this stored rotational energy is abruptly ejected. And even if neither neutron star is spinning, the authors show that magnetic flux twist still builds up and releases as a result of the binary’s orbital motion, assuming that the magnetic fields of the two stars are not aligned.

Here, the twisted flux tube and resultant flaring is caused by orbital motion of 45° misaligned magnetic fields, rather than by one star spinning. The bottom panel shows a 3D visualization of the field line configuration at the time of flaring. [Most & Philippov 2020]. Hi-res Image

Look for Radio Clues

So can we observe these sudden releases of energy? Most and Philippov argue that we should be able to spot the drama in radio emission: a radio afterglow will be produced behind the magnetized bubble that’s ejected from the twisted loop, and additional radio emission can be produced when the bubble collides with surrounding plasma.

Future work on this topic will explore the impacts of the neutron stars’ inspiral, and how the interactions of the magnetospheres change when the neutron stars carry unequal charge. The current study, however, indicates it’s worth keeping a radio eye out to see if we can spot signs of collisions to come!

Citation

“Electromagnetic Precursors to Gravitational-wave Events: Numerical Simulations of Flaring in Pre-merger Binary Neutron Star Magnetospheres,” Elias R. Most and Alexander A. Philippov 2020 ApJL 893 L6. doi:10.3847/2041-8213/ab8196

Source: American Astronomical Society (AAS)

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ESO Instrument Finds Closest Black Hole to Earth

PR Image eso2007a

Artist’s impression of the triple system with the closest black hole

PR Image eso2007b

Location of the HR 6819 in the constellation of Telescopium

PR Image eso2007c

Wide-field view of the region of the sky where HR 6819 is located

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Videos

PR Video eso2007a

ESOcast 220 Light: Closest Black Hole to Earth Found

PR Video eso2007b

Artist’s animation of the triple system with the closest black hole

PR Video eso2007c

Zooming into HR 6819

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 Invisible object has two companion stars visible to the naked eye

A team of astronomers from the European Southern Observatory (ESO) and other institutes has discovered a black hole lying just 1000 light-years from Earth. The black hole is closer to our Solar System than any other found to date and forms part of a triple system that can be seen with the naked eye. The team found evidence for the invisible object by tracking its two companion stars using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. They say this system could just be the tip of the iceberg, as many more similar black holes could be found in the future.

"We were totally surprised when we realised that this is the first stellar system with a black hole that can be seen with the unaided eye,” says Petr Hadrava, Emeritus Scientist at the Academy of Sciences of the Czech Republic in Prague and co-author of the research. Located in the constellation of Telescopium, the system is so close to us that its stars can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope. “This system contains the nearest black hole to Earth that we know of,” says ESO scientist Thomas Rivinius, who led the study published today in Astronomy & Astrophysics.

The team originally observed the system, called HR 6819, as part of a study of double-star systems. However, as they analysed their observations, they were stunned when they revealed a third, previously undiscovered body in HR 6819: a black hole. The observations with the FEROS spectrograph on the MPG/ESO 2.2-metre telescope at La Silla showed that one of the two visible stars orbits an unseen object every 40 days, while the second star is at a large distance from this inner pair.

Dietrich Baade, Emeritus Astronomer at ESO in Garching and co-author of the study, says: “The observations needed to determine the period of 40 days had to be spread over several months. This was only possible thanks to ESO’s pioneering service-observing scheme under which observations are made by ESO staff on behalf of the scientists needing them.”

The hidden black hole in HR 6819 is one of the very first stellar-mass black holes found that do not interact violently with their environment and, therefore, appear truly black. But the team could spot its presence and calculate its mass by studying the orbit of the star in the inner pair. “An invisible object with a mass at least 4 times that of the Sun can only be a black hole,” concludes Rivinius, who is based in Chile.

Astronomers have spotted only a couple of dozen black holes in our galaxy to date, nearly all of which strongly interact with their environment and make their presence known by releasing powerful X-rays in this interaction. But scientists estimate that, over the Milky Way’s lifetime, many more stars collapsed into black holes as they ended their lives. The discovery of a silent, invisible black hole in HR 6819 provides clues about where the many hidden black holes in the Milky Way might be. “There must be hundreds of millions of black holes out there, but we know about only very few. Knowing what to look for should put us in a better position to find them,” says Rivinius. Baade adds that finding a black hole in a triple system so close by indicates that we are seeing just “the tip of an exciting iceberg.”

Already, astronomers believe their discovery could shine some light on a second system. “We realised that another system, called LB-1, may also be such a triple, though we'd need more observations to say for sure,” says Marianne Heida, a postdoctoral fellow at ESO and co-author of the paper. "LB-1 is a bit further away from Earth but still pretty close in astronomical terms, so that means that probably many more of these systems exist. By finding and studying them we can learn a lot about the formation and evolution of those rare stars that begin their lives with more than about 8 times the mass of the Sun and end them in a supernova explosion that leaves behind a black hole."

The discoveries of these triple systems with an inner pair and a distant star could also provide clues about the violent cosmic mergers that release gravitational waves powerful enough to be detected on Earth. Some astronomers believe that the mergers can happen in systems with a similar configuration to HR 6819 or LB-1, but where the inner pair is made up of two black holes or of a black hole and a neutron star. The distant outer object can gravitationally impact the inner pair in such a way that it triggers a merger and the release of gravitational waves. Although HR 6819 and LB-1 have only one black hole and no neutron stars, these systems could help scientists understand how stellar collisions can happen in triple star systems.

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More information

This research was presented in the paper “A naked-eye triple system with a nonaccreting black hole in the inner binary”, published today in Astronomy & Astrophysics (doi: 10.1051/0004-6361/202038020).

The team is composed of Th. Rivinius (European Southern Observatory, Santiago, Chile), D. Baade (European Southern Observatory, Garching, Germany [ESO Germany]), P. Hadrava (Astronomical Institute, Academy of Science of the Czech Republic, Prague, Czech Republic), M. Heida (ESO Germany), and R. Klement (The CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, USA).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

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Links

• Research paper
• Photos of the MPG/ESO 2.2-metre telescope
• Photos of ESO’s La Silla Observatory

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Contacts

Dietrich Baade
European Southern Observatory
Garching bei München, Germany
Tel: +49-89-6096295
Email: dbaade@eso.org

Petr Hadrava
Academy of Sciences of the Czech Republic
Prague, Czech Republic
Email: petr.hadrava@asu.cas.cz

Marianne Heida
European Southern Observatory
Garching bei München, Germany
Tel: +49-157-37744840
Email: mheida@eso.org

Thomas Rivinius
European Southern Observatory
Santiago, Chile
Tel: +56 9 8288 4950
Email: triviniu@eso.org

Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Cell: +49 151 241 664 00
Email: pio@eso.org

Source: ESO/News

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Signals from Neutron Star Binaries

Artist's illustration of a binary star system consisting of two highly magnetized neutron stars.

Credit: John Rowe Animations

Fast radio bursts (FRBs) are brief radio signals that last on the order of milliseconds. They appear to be extragalactic, coming from small, point-like areas on the sky. Some FRBs are one-off events, while others are periodic or “repeating”. The sources of FRBs are still unknown, but binary neutron star systems might be a piece of the puzzle.

Wanted: A Reliable Source of Repeating Fast Radio Bursts

Any proposed model for a repeating FRB must explain a number of observed behaviors. Among them are the following:

1. Repeating bursts from a given FRB source are consistent in frequency and overall intensity on the timescale of years.
2. Bursts exhibit small-scale variations in measures of the source’s magnetic environment.
3. FRBs seem to be preferentially hosted in massive, Milky-Way-like galaxies.

Example of an FRB from a repeating source, showing the intensity and various frequencies contained in a single burst (darker means more intense, lighter means less intense). The red lines just below and above 550 MHz and those near 450 MHz and 650 MHz indicate frequencies that were unused due to other radio signals interfering [adapted from the CHIME/FRB Collaboration, Andersen et al.2019].

Binary neutron stars (BNSs) have been considered as possible solutions to the repeating FRB puzzle. Specifically, binary neutron star mergers might producIn a recent study, Bing Zhang (University of Nevada Las Vegas; Kyoto University, Japan) attempts to explain repeating FRBs using BNSs in a novel way. Instead of considering the neutron-star merger itself, Zhang examined whether the years leading up to the merger could produce repeating FRBs.e FRBs, along with gamma-ray bursts and gravitational waves. But how could BNSs produce repeating, consistent FRBs?

In a recent study, Bing Zhang (University of Nevada Las Vegas; Kyoto University, Japan) attempts to explain repeating FRBs using BNSs in a novel way. Instead of considering the neutron-star merger itself, Zhang examined whether the years leading up to the merger could produce repeating FRBs.

A Magnetic Dance

Repeating FRBs put out an enormous amount of energy over a few milliseconds — at least as much energy as the Sun puts out over three days. To put constraints on the average FRB-producing BNS, Zhang used the double-pulsar system PSR J0737-3039A/B (pulsars are fast-rotating neutron stars with strong magnetic fields), which is very well characterized in terms of its component stars and overall structure.

Aside from having enormous amounts of rotational energy intrinsically and in their orbits, BNSs also have strong magnetic fields. These magnetic fields are key to the production of FRBs in Zhang’s scenario — as the neutron stars orbit each other, their magnetic fields interact, possibly triggering a flow of particles that would produce FRBs.

On the scale of centuries or even decades pre-merger, these triggers could occur repeatedly and consistently, satisfying a key requirement for repeating FRBs. This picture of interacting magnetic fields would also explain the small-scale variations in the magnetic environment measures, and there is an overlap between the sorts of galaxies that host FRBs and those that host the gamma-ray bursts that could be associated with BNS mergers.

By Way of Gravitational Waves

An observational test for this scenario is the detection of gravitational waves from an FRB source. Space-based gravitational wave detectors, such as the Laser Interferometer Space Antenna, would be well-suited for this. Ground-based detectors would also play a role, picking up waves from the BNSs actually merging.

And of course, the more FRBs we observe, the more we can narrow down their properties and sources. Fortunately, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) is predicted to detect 2 to 50 FRBs per day, and other radio telescopes are hard at work as well. So maybe this FRB mystery will be solved sooner than we think!

Citation

“Fast Radio Bursts from Interacting Binary Neutron Star Systems,” Bing Zhang 2020 ApJL 890 L24. https://doi.org/10.3847/2041-8213/ab7244

By Tarini Konchady

Source: American Astronomical Society (AAS)

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LIGO-Virgo Network Catches Another Neutron Star Collision

GW190425 : Artist's impression of the binary neutron star merger observed by LIGO Livingston on April 25, 2019. Image credit: National Science FounGW190425 : Artist's impression of the binary neutron star merger observed by LIGO Livingston on April 25, 2019. Image credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet. dation/LIGO/Sonoma State University/A. Simonnet.

On April 25, 2019, the LIGO Livingston Observatory picked up what appeared to be gravitational ripples from a collision of two neutron stars. LIGO Livingston is part of a gravitational-wave network that includes LIGO (the Laser Interferometer Gravitational-wave Observatory), funded by the National Science Foundation (NSF), and the European Virgo detector. Now, a new study confirms that this event was indeed likely the result of a merger of two neutron stars. This would be only the second time this type of event has ever been observed in gravitational waves.

The first such observation, which took place in August of 2017, made history as the first joint observation of the same cosmic event in both gravitational waves and light. The April 25 merger, by contrast, did not result in any light being detected. However, through an analysis of the gravitational-wave data alone, researchers have learned that the objects involved in this collision were unusually massive given the expectations for neutron star binaries.

"From conventional observations with light, we already knew of 17 binary neutron star systems in our own galaxy and we have estimated the masses of these stars", says Ben Farr, a LIGO team member based at the University of Oregon. "What's surprising is that the combined mass of this binary is much higher than what was expected."

"We have detected a second event consistent with a binary neutron star system and this is an important confirmation of the August 2017 event that marked an exciting new beginning for multi-messenger astronomy two years ago", says Jo van den Brand, Virgo Spokesperson and professor at Maastricht University, and Nikhef and VU University Amsterdam in the Netherlands. Multi-messenger astronomy occurs when different types of signals are witnessed simultaneously, such as those based on gravitational waves and light.

The study, accepted for publication in The Astrophysical Journal Letters, is authored by an international team comprised of the LIGO Scientific Collaboration and the Virgo Collaboration, the latter of which is associated with the Virgo gravitational-wave detector in Italy.

Neutron stars are the remnants of dying stars that undergo catastrophic explosions as they collapse at the end of their lives. When two neutron stars spiral together, they undergo a violent merger that sends gravitational shudders through the fabric of space and time.

LIGO became the first observatory to directly detect gravitational waves in 2015; in that instance, the waves were generated by the violent collision of two black holes. Since then, LIGO and Virgo have registered dozens of additional candidate black hole mergers.

“Just as the first gravitational wave detection revealed a binary of unexpectedly massive black holes, this detection again reveals an unexpected member of the ‘cosmological ecosystem’ ”, says Nathan Johnson-McDaniel from the Department of Applied Mathematics and Theoretical Physics (DAMTP) at the University of Cambridge. “It is yet another illustration of the great discovery potential of gravitational wave observations.”

GW190425 FactSheet

Hi-res image

The April 2019 event was first identified in data from the LIGO Livingston detector alone. The LIGO Hanford detector was temporarily offline at the time, and, at a distance of more than 500 million light-years, the event was extremely faint in Virgo's data. Using the Livingston data, combined with information derived from Virgo’s data, the team narrowed the location of the event to a patch of sky more than 8,200 square degrees in size, or about 20 percent of the sky. For comparison, the August 2017 event was narrowed to a region of just 16 square degrees, or 0.04 percent of the sky.

“But what was the fate of this merger, what type of remnant did it leave behind?”, wonders Michalis Agathos, researcher at DAMTP and the Kavli Institute for Cosmology in Cambridge. “To answer this we can make use of information on the properties of neutron-star matter, that we had gained from the first event back in 2017. And we infer that the binary of this second event seems to be massive enough to immediately collapse upon merger, forming a black hole. Hence we should not expect a strong electromagnetic afterglow.”

The LIGO data reveal that the combined mass of the merged bodies is about 3.4 times the mass of our Sun. In our galaxy, known binary neutron star systems have combined masses up to only 2.9 times that of the Sun. One possibility for the unusually high mass is that the collision took place not between two neutron stars, but a neutron star and a black hole (black holes can be heavier than neutron stars). In this case, however, the black hole would be too light to match astrophysical observations and theoretical expectations. Therefore, the scientists believe it is much more likely that LIGO witnessed a merger of two neutron stars.

“When you look at the black holes and neutron stars observed so far, however, there is a gap in their mass distributions”, says Ulrich Sperhake head of the Cambridge LIGO group at DAMTP. “You have the black holes on the heavy end, the neutron stars on the light end and seemingly no objects in between with about 2.5 to 5 solar masses. This detection may give us the first clues whether and how this gap is filled.”

“This second event was consistent with matter properties extracted from the first binary neutron star observation, GW170817, but was not as loud”, said Charalampos Markakis from the University of Cambridge. “Future events and detector upgrades will allow us to measure properties of matter at extreme densities, beyond the reach of terrestrial laboratories, expanding our understanding of high-energy physics.”

Neutron star pairs are thought to form in two possible ways. They might form from binary systems of massive stars that each end their lives as neutron stars, or they might arise when two separately formed neutron stars come together within a dense stellar environment. The LIGO data for the April 25 event do not indicate which of these scenarios is more likely, but they do suggest that more data and new models are needed to explain the merger’s unexpectedly high mass.

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Additional information about the gravitational-wave observatories:

LIGO is funded by the NSF and operated by Caltech and MIT, which conceived of LIGO and lead the project. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. Approximately 1,300 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.

The Virgo Collaboration is currently composed of approximately 520 members from 99 institutes in 11 different countries including Belgium, France, Germany, Hungary, Italy, the Netherlands, Poland, and Spain. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and Nikhef in the Netherlands. A list of the Virgo Collaboration groups can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at http://www.virgo-gw.eu.

Source: Kavli Institute for Cosmology, Cambridge (KICC)/News

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Measuring the Age of the Universe

An artist's visualization of the merger of a binary neutron star. Gravitational waves from the mergers of binary neutron stars and binary black holes have recently been detected by the LIGO and Virgo facilities. These measurements can be used to calculate the age of the universe in a way that is independent of the two conventional methods previously used. Astronomers have calculated that in the next five years it is probable that fifty such events will be detected; their statistics will enable able an age determination with a precision of 2%, enough to also resolve the current incompatibility between the other two estimates. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet. Low Resolution (jpg)

Cambridge, MA - The single most important puzzle in today's cosmology (the study of the universe as a whole) can be summarized in one question: How old is it? For nearly a century -- since the discoveries by Einstein, Hubble, LeMaitre and others led to the big bang model of creation -- we have known the answer. It is about 13.8 billion years old (using current data). But in just the past decade the two alternative measurement methods have narrowed the uncertainties in their results to a few percent to reach a stunning conclusion: The two do not agree with each other. Since both methods are based on exactly the same model and equations, our understanding of the universe is somehow wrong -- perhaps fundamentally so.

Enter the most exciting technical achievement in astronomy for decades, the detection of gravitational waves (GW) caused by the mergers of black holes or neutron stars with each other by LIGO-Virgo, soon to be joined by other similar GW detection facilities in other countries. The solution to the cosmological dilemma is likely to be settled soon by these instruments according to a new Nature paper by Hsin-Yu Chen of Harvard's Black Hole Initiative, Maya Fishbach and Daniel E. Holz of the University of Chicago. The authors describe how upcoming detections of GW will have enough statistics to settle the question of age, forcing either one or the other (or perhaps even both) methods to re-think their basic understanding, or possibly even forcing a new variation of the When and How of the creation.

The two currently conflicting methods rely on observations of vastly different parts of the cosmic order. The first method measures and models the cosmic microwave background radiation (the CMBR method) produced by the universe when, after about 380,000 years, it cooled down and allowed neutral hydrogen atoms to form and light to propagate without scattering. The second method, the one used by Hubble and interpreted by LeMaitre, measures galaxies. This method takes advantage of the expansion of the universe to correlate a galaxy’s distance with its recession velocity, the so-called Hubble-LeMaitre Law, and to derive the Hubble-LeMaitre parameter which describes how long these galaxies have been in motion, related to the age of the universe. All astronomers today rely on this expression to obtain the distances to galaxies too far away to measure directly but whose velocities are easily seen in the Doppler shifts (the redshift) of their spectral lines. While the most familiar use of the parameter is to obtain the age of the universe, its value influences all the other parameters in the cosmological model (about nine of them) which together also explain the shape and expansion character of the universe.

Hubble calibrated his set of distances with nearby galaxies, but today we are capable of seeing galaxies so remote their light has been traveling to us for over ten billion years. Supernovae (SN), or at least those whose brightness is thought to be well understood, can be seen at great distances and so have been used to bootstrap the distance scale calibration outward from Hubble’s original neighborhood. There are subtle complexities in SN that are not well understood, however, resulting in an uncertainty that has been getting smaller as our understanding of them has improved. Today those uncertainties are small enough to exclude the comparable result from CMBR measurements.

The GW method of distance measurement is completely independent of both galaxy and CMBR methods. General relativity alone provides the intrinsic strength of the GW signal from its peculiar ringing signal, and its observed strength provides a direct measure of its distance. (The velocity information is obtained from the redshift of atomic lines in the host galaxy). Dr. Chen and her colleagues simulated 90,000 merger events in binary black hole or binary neutron star systems, including the host galaxy properties, and included likely selection effects and other complexities. The GW strength, for example, depends on our viewing angle of inclination of the merger, while the number of events to expect is only roughly constrained by the detections so far. Including these and similar uncertainties, the astronomers conclude that within the next five years it is likely that the GW method will fix the Hubble-LeMaitre parameter (that is, the age of the universe) to a precision of 2%, and to 1% in a decade, good enough to exclude one or even both of the other methods. The new paper's conclusions are bolstered by the fact that one paper using the GW method to estimate an age has already appeared. It had an uncertainty of between 11.9 billion years to 15.7 billion years, spanning both the current CMBR and galaxy values. But the new paper shows that in five years another roughly fifty GW events will be detected and these should be enough to settle the matter … and usher in a new era in precision cosmology.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

Tyler Jump
Public Affairs
Harvard-Smithsonian Center for Astrophysics
+1 617-495-7462
tyler.jump@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics (CfA)/News

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