Hubble celebrates Halloween with a glowering, dying star

CW Leonis

Credit: Image: ESA/Hubble, NASA, Toshiya Ueta (University of Denver), Hyosun Kim (KASI)

Release images | Release videos

---

A hypnotizing vortex? A peek into a witch's cauldron? A giant space-spider web?

In reality, it's a look at the red giant star CW Leonis as photographed by NASA's Hubble Space Telescope — just in time for celebrating Halloween with creepy celestial sights.

The orange-red "cobwebs" are dusty clouds of sooty carbon engulfing the dying star. They were created from the outer layers of CW Leonis being thrown out into the inky black void. The carbon, cooked up through nuclear fusion in the star's interior, gives it a carbon-rich atmosphere. Blasting the carbon back into space provides raw material for the formation of future stars and planets. All known life on Earth is built around the carbon atom. Complex biological molecules consist of carbon atoms bonded with other common elements in the universe.

At a distance of 400 light-years from Earth, CW Leonis is the closest carbon star. This gives astronomers the chance to understand the interplay between the star and its surrounding, turbulent envelope. The complex inner structure of shells and arcs may be shaped by the star’s magnetic field. Detailed Hubble observations of CW Leonis taken over the last two decades also show the expansion of threads of ejected material around the star.

The bright beams of light radiating outwards from CW Leonis are one of the star's most intriguing features. They've changed in brightness within a 15-year period — an incredibly short timespan in astronomical terms. Astronomers speculate that gaps in the dust shrouding CW Leonis may allow beams of starlight to pierce through and illuminate dust, like searchlight beacons through a cloudy sky. However, the exact cause of the dramatic changes in their brightness is as yet unexplained.

A star shines when the outward pressure from the fusion furnace at the core balances against the crush of gravity. When the star runs out of hydrogen fuel, the persistent pull of gravity causes the star to start collapsing. As the core shrinks, the shell of plasma surrounding the core becomes hot enough to begin fusing hydrogen, giving the star a second lease on life. It generates enough heat to dramatically expand the star's outer layers and swell up into a bloated red giant.

CW Leonis has an orange-reddish color due to its relatively low surface temperature of 2,300 degrees Fahrenheit. The green-tinted beams of light emanating from the star, however, glow at invisible mid-infrared wavelengths. In the absence of natural color, green has been added to the infrared image for better analysis through color-contrast.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

Credits: 

Release: ESA/Hubble, NASA, Toshiya Ueta (University of Denver), Hyosun Kim (KASI)

Media Contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Bethany Downer
ESA/Hubble.org

Science Contact:

Toshiya Ueta
University of Denver, Denver, Colorado

Hyosun Kim
Korea Astronomy and Space Science Institute, Daejeon, South Korea


Contact us:

Direct inquiries to the News Team.

Related links and documents:

• NASA's Hubble Portal
• ESA/Hubble's Release
• Goddard's "Hubble Spotted Something Scary" Video (on YouTube)

Source: HubbleSite/News

---

Amateur astronomers help discovery of a warped disc around a black hole in Milky Way

Black hole with warped disc

Credit John Paice

An international team of astrophysicists from South Africa, the UK, France and the US have found large variations in the brightness of light seen from around one of the closest black holes in our Galaxy, 9,600 light-years from Earth, which they conclude is caused by a huge warp in its accretion disc.
This object, MAXI J1820+070, erupted as a new X-ray transient in March 2018 and was discovered by a Japanese X-ray telescope onboard the International Space Station. These transients, systems that exhibit violent outbursts, are binary stars, consisting of a low-mass star, similar to our Sun and a much more compact object, which can be a white dwarf, neutron star or black hole. In this case, MAXI J1820+070 contains a black hole that is at least 8 times the mass of our Sun.

The first findings have now been accepted for publication in the international highly ranked journal, Monthly Notices of the Royal Astronomical Society, whose lead author is Dr Jessymol Thomas, a Postdoctoral Research Fellow at the South African Astronomical Observatory (SAAO).

The discovery presented in the paper was made from an extensive and detailed light-curve obtained over almost a year by dedicated amateurs around the globe who are part of the AAVSO (American Association of Variable Star Observers). MAXI J1820+070 is one of the three brightest X-ray transients ever observed, a consequence of both its proximity to Earth and being outside of the obscuring plane of our Milky Way Galaxy. Because it remained bright for many months, this made it possible to be followed by so many amateurs.

Professor Phil Charles, researcher at the University of Southampton and member of the research team explained, “material from the normal star is pulled by the compact object into its surrounding accretion disc of spiralling gas. Massive outbursts occur when the material in the disc becomes hot and unstable, accretes onto the black hole and releases copious amounts of energy before traversing the event horizon. This process is chaotic and highly variable, varying on timescales from milliseconds to months.”

The research team have produced a visualisation of the system, showing how a huge X-ray output emanates from very close to the black hole, and then irradiates the surrounding matter, especially the accretion disc, heating it up to a temperature of around 10,000K, which is seen as the visual light emitted. That is why, as the X-ray outburst declines, so does the optical light.

But something unexpected happened almost 3 months after the outburst began when the optical light curve started a huge modulation – a bit like turning a dimmer switch up and down and almost doubling in brightness at its peak - on a period of about 17 hours. Yet there was no change whatsoever in the X-ray output, which remained steady. While small, quasi-periodic visible modulations had been seen in the past during other X-ray transient outbursts, nothing on this scale had ever been seen before.

What was causing this extraordinary behaviour? “With the angle of view of the system as shown in the pictorial, we could quite quickly rule out the usual explanation that the X-rays were illuminating the inner face of the donor star because the brightening was occurring at the wrong time”, said Prof. Charles. Nor could it be due to varying light from where the mass transfer stream hits the disc as the modulation gradually moved relative to the orbit.

This left only one possible explanation, the huge X-ray flux was irradiating the disc and causing it to warp, as shown in the picture. The warp provides a huge increase in the area of the disc that could be illuminated, thereby making the visual light output increase dramatically when viewed at the right time. Such behaviour had been seen in X-ray binaries with more massive donors, but never in a black-hole transient with a low mass donor like this. It opens a completely new avenue for studying the structure and properties of warped accretion discs.

Prof Charles continued, “This object has remarkable properties amongst an already interesting group of objects that have much to teach us about the end-points of stellar evolution and the formation of compact objects. We already know of a couple of dozen black hole binary systems in our Galaxy, which all have masses in the 5 – 15 solar mass range. They all grow by the accretion of matter that we have witnessed so spectacularly here.”

Starting some 5 years ago, a major science programme on the Southern African Large Telescope (SALT) to study transient objects has made a number of important observations of compact binaries, including black hole systems like MAXI J1820+070. As the Principal Investigator for this programme, Prof. Buckley, states “SALT is a perfect tool to study the changing behaviour of these X-ray binaries during their outbursts, which it can monitor regularly over periods of weeks to months and can be coordinated with observations from other telescopes, including space-based ones.”

Source: University of Southampton/News

---

NASA’s Webb Will Join Forces with the Event Horizon Telescope to Reveal the Milky Way’s Supermassive Black Hole

An enormous swirling vortex of hot gas glows with infrared light, marking the approximate location of the supermassive black hole at the heart of our Milky Way galaxy. This multiwavelength composite image includes near-infrared light captured by NASA’s Hubble Space Telescope, and was the sharpest infrared image ever made of the galactic center region when it was released in 2009. Dynamic flickering flares in the region immediately surrounding the black hole, named Sagittarius A*, have complicated the efforts of the Event Horizon Telescope (EHT) collaboration to create a closer, more detailed image. While the black hole itself does not emit light and so cannot be detected by a telescope, the EHT team is working to capture it by getting a clear image of the hot glowing gas and dust directly surrounding it. NASA’s upcoming James Webb Space Telescope, scheduled to launch in December 2021, will combine Hubble’s resolution with even more infrared light detection. In its first year of science operations, Webb will join with EHT in observing Sagittarius A*, lending its infrared data for comparison to EHT’s radio data, making it easier to determine when bright flares are present, producing a sharper overall image of the region. In the composite image shown here, colors represent different wavelengths of light. Hubble’s near-infrared observations are shown in yellow, revealing hundreds of thousands of stars, stellar nurseries, and heated gas. The deeper infrared observations of NASA’s Spitzer Space Telescope are shown in red, revealing even more stars and gas clouds. Light detected by NASA’s Chandra X-ray Observatory is shown in blue and violet, indicating where gas is heated to millions of degrees by stellar explosions and by outflows from the supermassive black hole. Credits: NASA, ESA, SSC, CXC, STScI.  Hi-res image

On isolated mountaintops across the planet, scientists await word that tonight is the night: The complex coordination between dozens of telescopes on the ground and in space is complete, the weather is clear, tech issues have been addressed—the metaphorical stars are aligned. It is time to look at the supermassive black hole at the heart of our Milky Way galaxy.

This “scheduling Sudoku,” as the astronomers call it, happens each day of an observing campaign by the Event Horizon Telescope (EHT) collaboration, and they will soon have a new player to factor in; NASA’s James Webb Space Telescope will be joining the effort. During Webb’s first slate of observations, astronomers will use its infrared imaging power to address some of the unique and persistent challenges presented by the Milky Way’s black hole, named Sagittarius A* (Sgr A*; the asterisk is pronounced as “star”).

In 2017, EHT used the combined imaging power of eight radio telescope facilities across the planet to capture the historic first view of the region immediately surrounding a supermassive black hole, in the galaxy M87. Sgr A* is closer but dimmer than M87’s black hole, and unique flickering flares in the material surrounding it alter the pattern of light on an hourly basis, presenting challenges for astronomers.

“Our galaxy’s supermassive black hole is the only one known to have this kind of flaring, and while that has made capturing an image of the region very difficult, it also makes Sagittarius A* even more scientifically interesting,” said astronomer Farhad Yusef-Zadeh, a professor at Northwestern University and principal investigator on the Webb program to observe Sgr A*.

The flares are due to the temporary but intense acceleration of particles around the black hole to much higher energies, with corresponding light emission. A huge advantage to observing Sgr A* with Webb is the capability of capturing data in two infrared wavelengths (F210M and F480M) simultaneously and continuously, from the telescope’s location beyond the Moon. Webb will have an uninterrupted view, observing cycles of flaring and calm that the EHT team can use for reference with their own data, resulting in a cleaner image.

The source or mechanism that causes Sgr A*’s flares is highly debated. Answers as to how Sgr A*’s flares begin, peak, and dissipate could have far-reaching implications for the future study of black holes, as well as particle and plasma physics, and even flares from the Sun.

“Black holes are just cool,” said Sera Markoff, an astronomer on the Webb Sgr A* research team and currently vice chairperson of EHT’s Science Council. “The reason that scientists and space agencies across the world put so much effort into studying black holes is because they are the most extreme environments in the known universe, where we can put our fundamental theories, like general relativity, to a practical test.”

Heated gas swirls around the region of the Milky Way galaxy’s supermassive black hole, illuminated in near-infrared light captured by NASA’s Hubble Space Telescope. Released in 2009 to celebrate the International Year of Astronomy, this was the sharpest infrared image ever made of the galactic center region. NASA’s upcoming James Webb Space Telescope, scheduled to launch in December 2021, will continue this research, pairing Hubble-strength resolution with even more infrared-detecting capability. Of particular interest for astronomers will be Webb’s observations of flares in the area, which have not been observed around any other supermassive black hole and the cause of which is unknown. The flares have complicated the Event Horizon Telescope (EHT) collaboration’s quest to capture an image of the area immediately surrounding the black hole, and Webb’s infrared data is expected to help greatly in producing a clean image.Credits: NASA, ESA, STScI, Q. Daniel Wang (UMass). Hi-res image

Black holes, predicted by Albert Einstein as part of his general theory of relativity, are in a sense the opposite of what their name implies—rather than an empty hole in space, black holes are the most dense, tightly-packed regions of matter known. A black hole’s gravitational field is so strong that it warps the fabric of space around itself, and any material that gets too close is bound there forever, along with any light the material emits. This is why black holes appear “black.” Any light detected by telescopes is not actually from the black hole itself, but the area surrounding it. Scientists call the ultimate inner edge of that light the event horizon, which is where the EHT collaboration gets its name.

The EHT image of M87 was the first direct visual proof that Einstein’s black hole prediction was correct. Black holes continue to be a proving ground for Einstein’s theory, and scientists hope carefully scheduled multi-wavelength observations of Sgr A* by EHT, Webb, X-ray, and other observatories will narrow the margin of error on general relativity calculations, or perhaps point to new realms of physics we don’t currently understand.

As exciting as the prospect of new understanding and/or new physics may be, both Markoff and Zadeh noted that this is only the beginning. “It’s a process. We will likely have more questions than answers at first,” Markoff said. The Sgr A* research team plans to apply for more time with Webb in future years, to witness additional flaring events and build up a knowledge base, determining patterns from seemingly random flares. Knowledge gained from studying Sgr A* will then be applied to other black holes, to learn what is fundamental to their nature versus what makes one black hole unique.

So the stressful scheduling Sudoku will continue for some time, but the astronomers agree it’s worth the effort. “It’s the noblest thing humans can do, searching for truth,” Zadeh said. “It’s in our nature. We want to know how the universe works, because we are part of the universe. Black holes could hold clues to some of these big questions.”

NASA’s Webb telescope will serve as the premier space science observatory for the next decade and explore every phase of cosmic history—from within our solar system to the most distant observable galaxies in the early universe, and everything in between. Webb will reveal new and unexpected discoveries, and help humanity understand the origins of the universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

By Leah Ramsay
Space Telescope Science Institute, Baltimore, Md.

Editor: Lynn Jenner

Source: NASA/Blacks Holes

---

Towards the detection of the nanohertz gravitational-wave background

Fig. 1: Artistic impression of the EPTA experiment. A coordinated network of European radio telescopes observed an array of pulsars distributed across the sky. The measured variation in the arrival time of the emitted pulses on Earth allows astronomers to study tiny variations in spacetime. These variations, called gravitational waves, still propagate the Universe from a distant past, when galaxies merged and the supermassive black holes in their centre orbited each other with a period of a few years to produce them. © M. Kramer (Max Planck Institute for Radio Astronomy)

Fig. 2: The Five Major European Radio Telescopes from left top to right bottom: Effelsberg Radio Telescope, Germany, Nancay Radio Telescope, France, Sardinia Radio Telescope, Italy, Westerbork Synthesis Radio Telescope, The Netherlands and Lovell Telescope, UK. © N. Tacken/Max Planck Institute for Radio Astronomy (Effelsberg), Letourneur and Nançay Observatory (Nançay), A. Holloway (Jodrell Bank), ASTRON (WSRT), G. Alvito/INAF (SRT)

The European Pulsar Timing Array provides a significant step forward

The European Pulsar Timing Array (EPTA) is a scientific collaboration bringing together teams of astronomers around the largest European radio telescopes, as well as groups specialized in data analysis and modelling of gravitational-wave (GW) signals. It has published a detailed analysis of a candidate signal for the since-long sought gravitational-wave background (GWB) due to in-spiraling supermassive black-hole binaries. Although a detection cannot be claimed yet, this represents another significant step in the effort to finally unveil GWs at very low frequencies, of order one billionth of a Hertz. In fact, the candidate signal has emerged from an unprecedented detailed analysis and using two independent methodologies. Moreover, the signal shares strong similarities with those found from the analyses of other teams.

The results were made possible thanks to the data collected over 24 years with five large-aperture radio telescopes in Europe (see Fig. 2). They include MPIfR’s 100-m Radio Telescope near Effelsberg in Germany, the 76-m Lovell Telescope in Cheshire/United Kingdom, the 94-m Nançay Decimetric Radio Telescope in France, the 64-m Sardinia Radio Telescope at Pranu Sanguni, Italy and the 16 antennas of the Westerbork Synthesis Radio Telescope in the Netherlands. In the observing mode of the Large European Array for Pulsars (LEAP), the EPTA telescopes are tied together to synthesize a fully steerable 200-m dish to greatly enhance the sensitivity of the EPTA towards gravitational waves.

Radiation beams from the pulsars’ magnetic poles circle around their rotational axes, and we observe them as pulses when they pass our line of sight, like the light of a distant lighthouse. Pulsar timing arrays (PTAs) are networks of very stably rotating pulsars, used as galactic-scale GW detectors. In particular, they are sensitive to very low frequency GWs in the billionth-of-a-Hertz regime. This will extend the GW observing window from the high frequencies (hundreds of Hertz) currently observed by the ground-based detectors LIGO/Virgo/KAGRA. While those detectors probe short lasting collisions of stellar-mass black holes and neutron stars, PTAs can probe GWs such as those emitted by systems of slowly in-spiraling supermassive black-hole binaries hosted at the centres of galaxies. The addition of the GWs released from a cosmic population of these binaries forms a GWB.

Dr. Jonathan Gair, Group Leader in the “Astrophysical and Cosmological Relativity” department at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam and co-author of the study says: “In analysing pulsar timing data, we are looking for a common red noise in the pulsars that is caused by a gravitational wave background. The fact that we are seeing such a red noise is very exciting, but we cannot yet say that it is caused by gravitational waves. The astrophysical implications of the detection of a gravitational wave background from a population of supermassive black holes would be profound. The amplitude and properties of this background are affected by the process through which galaxies assemble and massive black hole binaries form and merge.”

However, the amplitude of the red noise is incredibly tiny (estimated to be tens to a couple hundreds of a billionth of a second) and in principle many other effects could impart that to any given pulsar in the PTA.

To validate the results, multiple independent codes with different statistical frameworks were then used to mitigate alternate sources of noise and search for the GWB.
Importantly, two independent end-to-end procedures were used in the analysis for cross-consistency. Additionally, three independent methods were used to account for possible systematics in the Solar-system planetary parameters used in the models predicting the pulse arrival times, a prime candidate for false-positive GW signals.

The EPTA analysis with both procedures found a clear candidate signal for a GWB and its spectral properties (i.e. how the amplitude of the observed noise varies with its frequency) remain within theoretical expectations for the noise attributable to a GWB.

Dr. Nicolas Caballero, researcher at the Kavli Institute for Astronomy and Astrophysics in Beijing and co-lead author explains: “The EPTA first found indications for this signal in their previously published data set in 2015, but as the results had larger statistical uncertainties, they were only strictly discussed as upper limits. Our new data now clearly confirm the presence of this signal, making it a candidate for a GWB“.

Einstein’s General Relativity predicts a very specific relation among the spacetime deformations experienced by the radio signals coming from pulsars located in different directions in the sky. Scientists call that as the spatial correlation of the signal, or Hellings and Downs curve. Its detection will uniquely identify the observed noise as due to a GWB. Dr. Siyuan Chen, researcher at the LPC2E, CNRS in Orleans, co-lead author of the study, notes “At the moment, the statistical uncertainties in our measurements do not allow us yet to identify the presence of spatial correlation expected for the gravitational-wave background signal. For further confirmation we need to include more pulsar data into the analysis, however the current results are very encouraging“.

The EPTA is a founding member of the International Pulsar Timing Array (IPTA). As analyses of independent data performed by the other IPTA partners (i.e. the NANOGrav and the PPTA experiments) also indicated similar common signals, it has become vital to apply multiple analysis algorithms to increase confidence in a possible future GWB detection. The IPTA members are working together, drawing conclusions from comparing their data and analyses to better prepare for the next steps.

“As the signal we are looking for is stochastic, it is easy to confuse it with other random processes occurring in the pulsars or in the instruments used to observe them”, says Lorenzo Speri, PhD student in the “Astrophysical and Cosmological Relativity” department and co-author of the study. “Separating the common red noise, which is our signal, from individual noises, requires careful statistical analysis.” And Jonathan Gair adds: “The statistical techniques have been carefully developed over the last decade and it is gratifying to see them finally yielding promising scientific results.”

Jonathan Gair has been a member of the EPTA for the past decade, working on developing the statistical formalism used to analyse EPTA data. Lorenzo Speri has been working on the analysis of EPTA data for the past year, including, among other things, the optimal selection of pulsars to use in the analysis. Over the coming year, Gair and Speri will be working on the analysis of the full EPTA data set, and the IPTA data set that combines this data with data from other pulsar timing collaborations. The hope is that these data sets, containing many more pulsars, might have sufficient sensitivity that the origin of the background may begin to be identified.

---

Media contact:

Dr. Elke Müller
Press Officer AEI Potsdam, Scientific Coordinator
tel:+49 331 567-7303
tel:+49 331 567-7298

Science contacts:

Dr. Jonathan Gair
Group Leader
tel:+49 331 567-7306
tel:+49 331 567-7298

Lorenzo Speri
PhD Student
tel:+49 331 567-7185
tel:+49 331 567-7298

---

Publication:

1. Chen, S.; Caballero, R. N.; Guo, Y. J.; Chalumeau, A.; Liu, K.; Shaifullah, G.; Lee, K. J.; Babak, S.; Desvignes, G.; Parthasarathy, A.; Hu, H.; van der Wateren, E.; Antoniadis, J.; Bak Nielsen, A.-S.; Bassa, C. G.; Berthereau, A.; Burgay, M.; Champion, D. J.; Cognard, I.; Falxa, M.; Ferdman, R. D.; Freire, P. C. C.; Gair, J. R.; Graikou, E.; Guillemot, L.; Jang, J.; Janssen, G. H.; Karuppusamy, R.; Keith, M. J.; Kramer, M.; Liu, X. J.; Lyne, A. G.; Main, R. A.; McKee, J.W.; Mickaliger, M. B.; Perera, B. B. P.; Perrodin, D.; Petiteau, A.; Porayko, N. K.; Possenti, A.; Samajdar, A.; Sanidas, S. A.; Sesana, A.; Speri, L.; Stappers, B. W.; Theureau, G.; Tiburzi, C.; Vecchio, A.; Verbiest, J. P. W.; Wang, J.; Wang, L. and Xu, H.

Common-red-signal analysis with 24-yr high-precision timing of the European Pulsar Timing Array: Inferences in the stochastic gravitational-wave background search Monthly Notices of the Royal Astronomical Society 508, 4970 (2021)

Source / DOI

---

Further Information:

Science Summary of the publication

European Pulsar Timing Array

Participating telescopes

• Effelsberg Radio Telescope
• Lovell Telescope
• Nançay Decimetric Radio Telescope
• Sardinia Radio Telescope
• Westerbork Synthesis Radio Telescope

Source: Max Planck Institute for Gravitational Physics/News

---

Neutron star collisions are a “goldmine” of heavy elements, study finds

New research suggests binary neutron stars are a likely cosmic source for the gold, platinum, and other heavy metals we see today. Credits: National Science Foundation/LIGO/Sonoma State University/A. Simonnet, edited by MIT News 

Mergers between two neutron stars have produced more heavy elements in last 2.5 billion years than mergers between neutron stars and black holes.

Most elements lighter than iron are forged in the cores of stars. A star’s white-hot center fuels the fusion of protons, squeezing them together to build progressively heavier elements. But beyond iron, scientists have puzzled over what could give rise to gold, platinum, and the rest of the universe’s heavy elements, whose formation requires more energy than a star can muster.

A new study by researchers at MIT and the University of New Hampshire finds that of two long-suspected sources of heavy metals, one is more of a goldmine than the other.

The study, published today in Astrophysical Journal Letters, reports that in the last 2.5 billion years, more heavy metals were produced in binary neutron star mergers, or collisions between two neutron stars, than in mergers between a neutron star and a black hole.

The study is the first to compare the two merger types in terms of their heavy metal output, and suggests that binary neutron stars are a likely cosmic source for the gold, platinum, and other heavy metals we see today. The findings could also help scientists determine the rate at which heavy metals are produced across the universe.

“What we find exciting about our result is that to some level of confidence we can say binary neutron stars are probably more of a goldmine than neutron star-black hole mergers,” says lead author Hsin-Yu Chen, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research.

Chen’s co-authors are Salvatore Vitale, assistant professor of physics at MIT, and Francois Foucart of UNH.

An efficient flash

As stars undergo nuclear fusion, they require energy to fuse protons to form heavier elements. Stars are efficient in churning out lighter elements, from hydrogen to iron. Fusing more than the 26 protons in iron, however, becomes energetically inefficient.

“If you want to go past iron and build heavier elements like gold and platinum, you need some other way to throw protons together,” Vitale says.

Scientists have suspected supernovae might be an answer. When a massive star collapses in a supernova, the iron at its center could conceivably combine with lighter elements in the extreme fallout to generate heavier elements.

In 2017, however, a promising candidate was confirmed, in the form a binary neutron star merger, detected for the first time by LIGO and Virgo, the gravitational-wave observatories in the United States and in Italy, respectively. The detectors picked up gravitational waves, or ripples through space-time, that originated 130 million light years from Earth, from a collision between two neutron stars — collapsed cores of massive stars, that are packed with neutrons and are among the densest objects in the universe.

The cosmic merger emitted a flash of light, which contained signatures of heavy metals.

“The magnitude of gold produced in the merger was equivalent to several times the mass of the Earth,” Chen says. “That entirely changed the picture. The math showed that binary neutron stars were a more efficient way to create heavy elements, compared to supernovae.”

A binary goldmine

Chen and her colleagues wondered: How might neutron star mergers compare to collisions between a neutron star and a black hole? This is another merger type that has been detected by LIGO and Virgo and could potentially be a heavy metal factory. Under certain conditions, scientists suspect, a black hole could disrupt a neutron star such that it would spark and spew heavy metals before the black hole completely swallowed the star.

The team set out to determine the amount of gold and other heavy metals each type of merger could typically produce. For their analysis, they focused on LIGO and Virgo’s detections to date of two binary neutron star mergers and two neutron star – black hole mergers.

The researchers first estimated the mass of each object in each merger, as well as the rotational speed of each black hole, reasoning that if a black hole is too massive or slow, it would swallow a neutron star before it had a chance to produce heavy elements. They also determined each neutron star’s resistance to being disrupted. The more resistant a star, the less likely it is to churn out heavy elements. They also estimated how often one merger occurs compared to the other, based on observations by LIGO, Virgo, and other observatories.

Finally, the team used numerical simulations developed by Foucart, to calculate the average amount of gold and other heavy metals each merger would produce, given varying combinations of the objects’ mass, rotation, degree of disruption, and rate of occurrence.

On average, the researchers found that binary neutron star mergers could generate two to 100 times more heavy metals than mergers between neutron stars and black holes. The four mergers on which they based their analysis are estimated to have occurred within the last 2.5 billion years. They conclude then, that during this period, at least, more heavy elements were produced by binary neutron star mergers than by collisions between neutron stars and black holes.

The scales could tip in favor of neutron star-black hole mergers if the black holes had high spins, and low masses. However, scientists have not yet observed these kinds of black holes in the two mergers detected to date.

Chen and her colleagues hope that, as LIGO and Virgo resume observations next year, more detections will improve the team’s estimates for the rate at which each merger produces heavy elements. These rates, in turn, may help scientists determine the age of distant galaxies, based on the abundance of their various elements.

“You can use heavy metals the same way we use carbon to date dinosaur remains,” Vitale says. “Because all these phenomena have different intrinsic rates and yields of heavy elements, that will affect how you attach a time stamp to a galaxy. So, this kind of study can improve those analyses.”

This research was funded, in part, by NASA, the National Science Foundation, and the LIGO Laboratory.

Jennifer Chu | MIT News Office

Source: MIT/News

---

Chandra Sees Evidence for Possible Planet in Another Galaxy

M51/Whirpool Galaxy

Credit X-ray: NASA/CXC/SAO/R. DiStefano, et al.; 

Optical: NASA/ESA/STScI/Grendler; 

Illustration: NASA/CXC/M.Weiss

JPEG (299.8 kb) - Large JPEG (12.4 MB) - Tiff (101 MB) - More Images

Tour: Chandra Sees Evidence for Possible Planet in Another Galaxy - More Animations

---

Astronomers have found evidence for a possible planet candidate in the M51 ("Whirlpool") galaxy, potentially representing what would be the first planet seen to transit a star outside of the Milky Way. As reported in our latest press release, researchers used NASA's Chandra X-ray Observatory to detect the dimming of X-rays from an "X-ray binary", a system where a Sun-like star is in orbit around a neutron star or black hole. The authors interpret this dimming as being a planet passing in front of the neutron star or black hole.

The left panel of this graphic shows M51 in X-rays from Chandra (purple and blue) and optical light from NASA's Hubble Space Telescope (red, green, and blue). A box marks the location of the possible planet candidate, an X-ray binary known as M51-ULS-1. An artist's illustration in the right panel depicts the X-ray binary and possible planet. Material from the companion star (white and blue in illustration) is pulled onto the neutron star or black hole, forming a disk around the dense object (illustrated as red and orange). The material near the dense object becomes superheated, causing it to glow in X-ray light (white). The planet is shown beginning to pass in front of this source of X-rays.

Looking for the dimming of a star's light as something passes in front of it is called the transit technique. For years, scientists have discovered exoplanets using transits with optical light telescopes, which detect the range of light humans can see with their eyes and more. This includes both ground-based telescopes and space-based ones like NASA's Kepler mission. These optical light transit detections require very high levels of sensitivity because the planet is much smaller than the star it passes in front of, and, therefore, only a tiny fraction of the light is blocked.

M51-ULS-1 Transit Only

Animation Credit: NASA/CXC/A.Jubett

The scenario of a transit in an X-ray binary is different. Because a potential planet is close in size to the X-ray source around the neutron star or black hole, a transiting planet passing along Earth's line of sight could temporarily block most or all of the X-rays. This makes it possible to spot transits at greater distances — including beyond the Milky Way — than current optical light studies using transits. A separate graphic shows how X-rays from M51-ULS-1 temporarily decrease to zero during the Chandra observations.

While this is a tantalizing study, the case of an exoplanet in M51 is not ironclad. One challenge is that the planet candidate's large orbit in M51-ULS-1 means it would not cross in front of its binary partner again for about 70 years, thwarting any attempts for a confirming observation for decades. There is also the possibility that the dimming of X-rays is due to a passing cloud of gas near the M51-ULS-1, though the researchers think the data strongly favor the planet explanation.

Illustration Credit: NASA/CXC/M. Weiss

The paper describing these results appears in the latest issue of Nature Astronomy and is available online. The authors are Rosanne DiStefano (CfA), Julia Berndtsson (Princeton), Ryan Urquhart (Michigan State University), Roberto Soria (University of the Chinese Science Academy), Vinay Kashap (CfA), Theron Carmichael (CfA), and Nia Imara (now at the University of California at Santa Cruz). NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.

Quick Look: Chandra Sees Evidence for Possible Planet in Another Galaxy

---

Fast Facts for M51/Whirlpool Galaxy:

Scale: Image is about 6 arcmin (49,000 light years) across.
Category: Normal Galaxies & Starburst Galaxies
Constellation: Canes Venatici
Observation Date: 11 pointings between March 2000 and October 2012
Observation Time: 232 hours 10 minutes (9 days 16 hours 10 min)
Obs. ID: 353, 354, 1622, 3932, 13812-13816, 15496, 15553
Instrument: ACIS
Also Known As: NGC 5194, NGC 5195
References: DiStefano, R., et al., 2021, Nature Astronomy (Published); PDF Document
Color Code: X-ray: purple and blue; Optical: red, green, and blue
Distance Estimate: About 28 million light years

Source: NASA's Chandra X-Ray Observatory

---

Astronomers Provide 'Field Guide' to Exoplanets Known as Hot Jupiters By Daniel Stolte, University Communications

This artist’s impression shows a hot Jupiter planet orbiting close to one of the stars in the rich old star cluster Messier 67, located between 2,500 and 3,000 light-years from Earth in the constellation of Cancer (The Crab).ESO/L. Calçada

The turbulent atmosphere of a hot, gaseous planet known as HD 80606b is shown in this simulation based on data from NASA's Spitzer Space Telescope. The planet spends most of its time far away from its star, but every 111 days, it swings extremely close to the star, experiencing a massive burst of heat.NASA/JPL-CalTech

By combining Hubble Space Telescope observations with theoretical models, a team of astronomers has gained insights into the chemical and physical makeup of a variety of exoplanets known as hot Jupiters. The findings provide a new and improved "field guide" for this group of planets and inform ideas about planet formation in general.

Hot Jupiters – giant gas planets that race around their host stars in extremely tight orbits – have become a little bit less mysterious thanks to a new study combining theoretical modeling with observations by the Hubble Space Telescope.

While previous studies mostly focused on individual worlds classified as "hot Jupiters" due to their superficial similarity to the gas giant in our own solar system, the new study is the first to look at a broader population of the strange worlds. Published in Nature Astronomy, the study, led by a University of Arizona researcher, provides astronomers with an unprecedented "field guide" to hot Jupiters and offers insight into planet formation in general.

Although astronomers think that only about 1 in 10 stars host an exoplanet in the hot Jupiter class, the peculiar planets make up a sizeable portion of exoplanets discovered to date, due to the fact that they are bigger and brighter than other types of exoplanets, such as rocky, more Earthlike planets or smaller, cooler gas planets. Ranging in size from about one-third the size of Jupiter to 10 Jupiter masses, all hot Jupiters orbit their host stars at an extremely close range, usually much closer than Mercury – the innermost planet in our solar system – is to the sun. A "year" on a typical hot Jupiter lasts hours, or at most a few days. For comparison, Mercury takes almost three months to complete a trip around the sun.

Because of their close orbits, most, if not all, hot Jupiters are thought to be locked in a high-speed embrace with their host stars, with one side eternally exposed to the star's radiation and the other shrouded in perpetual darkness. The surface of a typical hot Jupiter can get as hot as almost 5,000 degrees Fahrenheit, with "cooler" specimens reaching 1,400 degrees – hot enough to melt aluminum.

The research, which was led by Megan Mansfield, a NASA Sagan Fellow at the University of Arizona's Steward Observatory, used observations made with the Hubble Space Telescope that allowed the team to directly measure emission spectra from hot Jupiters, despite the fact that Hubble can't image any of these planets directly.

"These systems, these stars and their hot Jupiters, are too far away to resolve the individual star and its planet," Mansfield said. "All we can see is a point – the combined light source of the two."

Mansfield and her team used a method known as secondary eclipsing to tease out information from the observations that allowed them to peer deep into the planets' atmospheres and gain insights into their structure and chemical makeup. The technique involves repeated observations of the same system, catching the planet at various places in its orbit, including when it dips behind the star.

"We basically measure the combined light coming from the star and its planet and compare that measurement with what we see when the planet is hidden behind its star," Mansfield said. "This allows us to subtract the star's contribution and isolate the light emitted by the planet, even though we can't see it directly."

The eclipse data provided the researchers with insight into the thermal structure of the atmospheres of hot Jupiters and allowed them to construct individual profiles of temperatures and pressures for each one. The team then analyzed near-infrared light, which is a band of wavelengths just beyond the range humans can see, coming from each hot Jupiter system for so-called absorption features. Because each molecule or atom has its own specific absorption profile, like a fingerprint, looking at different wavelengths allows researchers to obtain information about the chemical makeup of hot Jupiters. For example, if water is present in the planet's atmosphere, it will absorb light at 1.4 microns, which falls into the range of wavelengths that Hubble can see very well.

"In a way, we use molecules to scan through the atmospheres on these hot Jupiters," Mansfield said. "We can use the spectrum we observe to get information on what the atmosphere is made of, and we can also get information on what the structure of the atmosphere looks like."

The team went a step further by quantifying the observational data and comparing it to models of the physical processes believed to be at work in the atmospheres of hot Jupiters. The two sets matched very well, confirming that many predictions about the planets' nature – based on theoretical work – appear to be correct, according to Mansfield, who said the findings are "exciting because they were anything but guaranteed."

The results suggest that all hot Jupiters, not just the 19 included in the study, are likely to contain similar sets of molecules, like water and carbon monoxide, along with smaller amounts of other molecules. The differences among individual planets should mostly amount to varying relative amounts of these molecules. The findings also revealed that the observed water absorption features varied slightly from one hot Jupiter to the next.

"Taken together, our results tell us there is a good chance we have the big picture items figured out that are happening in the chemistry of these planets," Mansfield said. "At the same time, each planet has its own chemical makeup, and that also influences what we see in our observations."

According to the authors, the results can be used to guide expectations of what astronomers might be able to see when looking at a hot Jupiter that hasn't been studied before. The launch of NASA's news flagship telescope, the James Webb Space Telescope, slated for Dec. 18, has exoplanet hunters excited because Webb can see in a much broader range of infrared light, and will allow a much more detailed look at exoplanets, including hot Jupiters.

"There is a lot that we still don't know about how planets form in general, and one of the ways we try to understand how that could happen is by looking at the atmospheres of these hot Jupiters and figuring out how they got to be where they are," Mansfield said. "With the Hubble data, we can look at trends by studying the water absorption, but when we are talking about the composition of the atmosphere as a whole, there are many other important molecules you want to look at, such as carbon monoxide and carbon dioxide, and JWST will give us a chance to actually observe those as well."

Resources for the Media 

Media contact:

Daniel Stolte
Science Writer, University Communications
stolte@arizona.edu
520-626-4402

Researcher contact:

Megan Mansfield
NASA Sagan Fellow, Steward Observatory
meganmansfield@arizona.edu

Source: The Arizona University/News

---

Hubble Watches an Intergalactic Dance

NGC 7752 and NGC 7753

mage credit: ESA/Hubble & NASA, Dark Energy Survey, J. Dalcanton

Text credit: European Space Agency (ESA)

This observation from the NASA/ESA Hubble Space Telescope showcases Arp 86, a peculiar pair of interacting galaxies which lies roughly 220 million light-years from Earth in the constellation Pegasus. Arp 86 is composed of the two galaxies NGC 7752 and NGC 7753 – NGC 7753 is the large spiral galaxy dominating this image, and NGC 7752 is its smaller companion. The diminutive companion galaxy almost appears attached to NGC 7753, and it is this peculiarity that has earned the designation “Arp 86” – signifying that the galaxy pair appears in the Atlas of Peculiar Galaxies compiled by the astronomer Halton Arp in 1966. The gravitational dance between the two galaxies will eventually result in NGC 7752 being tossed out into intergalactic space or entirely engulfed by its much larger neighbor.

Hubble observed Arp 86 as part of a larger effort to understand the connections between young stars and the clouds of cold gas in which they form. Hubble gazed into star clusters and clouds of gas and dust in a variety of environments dotted throughout nearby galaxies. Combined with measurements from ALMA, a gigantic radio telescope perched high in the Chilean Andes, these Hubble observations provide a treasure trove of data for astronomers working to understand how stars are born.

These observations also helped sow the seeds of future research using the NASA/ESA James Webb Space Telescope. Due to launch later this year, Webb will study star formation in dusty regions like those in the galaxies of Arp 86.

Media Contact:

Claire Andreoli
NASA's Goddard Space Flight Center
301-286-1940

Editor: Lynn Jenner

Source: NASA/Hubble

---

Hubble gives unprecedented, early view of a doomed star's destruction

Astronomers recently witnessed supernova SN 2020fqv explode inside the interacting Butterfly galaxies, located about 60 million light-years away in the constellation Virgo. Researchers quickly trained NASA's Hubble Space Telescope on the aftermath. Along with other space- and ground-based telescopes, Hubble delivered a ringside seat to the first moments of the ill-fated star's demise, giving a comprehensive view of a supernova in the very earliest stage of exploding. Hubble probed the material very close to the supernova that was ejected by the star in the last year of its life. These observations allowed researchers to understand what was happening to the star just before it died, and may provide astronomers with an early warning system for other stars on the brink of death. Credits: Author: NASA, ESA, Ryan Foley (UC Santa Cruz)-Image processingM: Joseph DePasquale (STScI). Release images

Like a witness to a violent death, NASA's Hubble Space Telescope recently gave astronomers an unprecedented, comprehensive view of the first moments of a star's cataclysmic demise. Hubble's data, combined with other observations of the doomed star from space- and ground-based telescopes, may give astronomers an early warning system for other stars on the verge of blowing up.

"We used to talk about supernova work like we were crime scene investigators, where we would show up after the fact and try to figure out what happened to that star," explained Ryan Foley of the University of California, Santa Cruz, the leader of the team that made this discovery. "This is a different situation, because we really know what's going on and we actually see the death in real time."

Telescope Teamwork

The supernova, called SN 2020fqv, is in the interacting Butterfly Galaxies, which are located about 60 million light-years away in the constellation Virgo. It was discovered in April 2020 by the Zwicky Transient Facility at the Palomar Observatory in San Diego, California. Astronomers realized that the supernova was simultaneously being observed by the Transiting Exoplanet Survey Satellite (TESS), a NASA satellite designed primarily to discover exoplanets, with the ability to detect an assortment of other phenomena. They quickly trained Hubble and a suite of ground-based telescopes on it.

Together, these observatories gave the first holistic view of a star in the very earliest stage of destruction. Hubble probed the material very close to the star, called circumstellar material, mere hours after the explosion. This material was blown off the star in the last year of its life. These observations allowed astronomers to understand what was happening to the star just before it died.

"We rarely get to examine this very close-in circumstellar material since it is only visible for a very short time, and we usually don't start observing a supernova until at least a few days after the explosion," explained Samaporn Tinyanont, lead author on the study's paper to be published in the Monthly Notices of the Royal Astronomical Society. "For this supernova, we were able to make ultra-rapid observations with Hubble, giving unprecedented coverage of the region right next to the star that exploded."

Telling the Star's Story

The team looked at Hubble observations of the star going back to the 1990s. TESS provided an image of the system every 30 minutes starting several days before the explosion, through the explosion itself, and continuing for several weeks. Hubble was used again starting only hours after astronomers first detected the explosion. And from studying the circumstellar material with Hubble, the scientists gained an understanding of what was happening around the star in the previous decade. By combining all of this information, the team was able to create a multi-decade look at the star's final years.

"Now we have this whole story about what's happening to the star in the years before it died, through the time of death, and then the aftermath of that," said Foley. "This is really the most detailed view of stars like this in their last moments and how they explode."

The Rosetta Stone of Supernovas

Tinyanont and Foley called SN 2020fqv "the Rosetta Stone of supernovas." The ancient Rosetta Stone, which has the same text inscribed in three different scripts, helped experts learn to read Egyptian hieroglyphs.

In the case of this supernova, the science team used three different methods to determine the mass of the exploding star. These included comparing the properties and the evolution of the supernova with theoretical models; using information from a 1997 archival Hubble image of the star to rule out higher-mass stars; and using observations to directly measure the amount of oxygen in the supernova, which probes the mass of the star. The results are all consistent: around 14 to 15 times the mass of the Sun. Accurately determining the mass of the star that explodes in a supernova is crucial to understanding how massive stars live and die.

"People use the term 'Rosetta Stone' a lot. But this is the first time we've been able to verify the mass with these three different methods for one supernova, and all of them are consistent," said Tinyanont. "Now we can push forward using these different methods and combining them, because there are a lot of other supernovas where we have masses from one method but not another."

An Early Warning System?

In the years before stars explode, they tend to become more active. Some astronomers point to the red supergiant Betelgeuse, which has recently been belching significant amounts of material, and they wonder if this star will soon go supernova. While Foley doubts Betelgeuse will imminently explode, he does think we should take such stellar outbursts seriously.

"This could be a warning system," said Foley. "So if you see a star start to shake around a bit, start acting up, then maybe we should pay more attention and really try to understand what's going on there before it explodes. As we find more and more of these supernovas with this sort of excellent data set, we'll be able to understand better what's happening in the last few years of a star's life."

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C. 

 Credits: Release: NASA, ESA

Media Contact:

Ann Jenkins
Space Telescope Science Institute, Baltimore, Maryland

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Science Contact:

Ryan Foley
University of California, Santa Cruz, Santa Cruz, California

Samaporn Tinyanont

University of California, Santa Cruz, Santa Cruz, California

Contact us:
Direct inquiries to the News Team.

Related links and documents:

Science Paper: The science paper by S. Tinyanont, PDF (8.83 MB)
NASA's Hubble Portal

Source: HubbleSite/News

---

Astronomers see white dwarf switch on and off

An artist’s impression example of a white dwarf – in this image the white dwarf MV Lyrae – accreting as it draws in material from a companion star. Credit: Helena Uthas

White dwarfs are what most stars become after burning off the hydrogen that fuels them. Now our astronomers have seen one of these galactic objects switching on and off for the first time.

Researchers used a planet-hunting satellite to observe the unique phenomenon in a white dwarf about 1,400 light years from Earth.

This particular white dwarf is known to be accreting, or feeding, from an orbiting companion star.

Our astronomers saw it lose brightness in 30 minutes, a process only previously seen in accreting white dwarfs over a period of several days to months.

Accreting white dwarf

The brightness of an accreting white dwarf is affected by the amount of surrounding material it feeds on so the researchers say something is interfering with its food supply.

They believe what they’re witnessing could be changes to the white dwarf’s surface magnetic field.

During the “on” mode, when the brightness is high, the white dwarf feeds off the accretion disc as it normally would.

Suddenly and abruptly the system turns “off” and its brightness plummets.

Magnetic gating

The researchers say that when this happens the magnetic field is spinning so rapidly it creates a barrier disrupting the amount of food the white dwarf can receive – a process called magnetic gating.

This leads to semi-regular small increases in brightness seen by the astronomers. After some time, the system sporadically turns “on” again, and the brightness increases back to its original level.

They hope their discovery will teach us more about the physics behind accretion – where objects like black holes, white dwarfs and neutron stars feed on surrounding material from neighbouring stars.

Find out more

• Read the full research paper in Nature Astronomy.
• Dr Simone Scaringi, in our Centre for Extragalactic Astronomy, led the study.
• Researchers observed the white dwarf binary system TW Pictoris using NASA’s Transiting Exoplanet Survey Satellite – normally used to spot planets outside of our solar system.
• See undergraduate and postgraduate opportunities in Physics at Durham.

Source:  Durhan University/News and Events

---

Studying the Edge of the Sun’s Magnetic Bubble

The heliosphere within the Milky Way galaxy.

Credits: NASA's Goddard Space Flight Center/Conceptual Image Lab/Walt Feimer

Our corner of the universe, the solar system, is nestled inside the Milky Way galaxy, home to more than 100 billion stars. The solar system is encased in a bubble called the heliosphere, which separates us from the vast galaxy beyond – and some of its harsh space radiation.

We’re protected from that radiation by the heliosphere, which itself is created by another source of radiation: the Sun. The Sun constantly spews charged particles, called the solar wind, from its surface. The solar wind flings out to about four times the distance of Neptune, carrying with it the magnetic field from the Sun.

“Magnetic fields tend to push up against each other, but not mix,” said Eric Christian, a lead heliosphere research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Inside the bubble of the heliosphere are pretty much all particles and magnetic fields from the Sun. Outside are those from the galaxy.”

To understand the heliosphere, start by breaking apart the word, suggests David McComas, professor of astrophysical sciences at Princeton University in New Jersey. "Heliosphere" is the combination of two words: "Helios," the Greek word for the Sun, and "sphere," a broad region of influence (though, to be clear, scientists aren’t sure of the heliosphere’s exact shape).

The heliosphere was discovered in the late 1950s, and many questions about it remain. As scientists study the heliosphere, they learn more about how it reduces astronauts’ and spacecrafts' exposure to radiation and more generally, how stars can influence their nearby planets.

The heliosphere changes in size throughout the solar cycle.

Credits: NASA's Goddard Space Flight Center/Scientific Visualization Studio/Tom Bridgman

A balloon in space

Some radiation surrounds us every day. When we sunbathe, we’re basking in radiation from the Sun. We use radiation to warm leftovers in our kitchen microwaves and rely on it for medical imaging.

Space radiation, however, is more similar to the radiation released by radioactive elements like uranium. The space radiation that comes at us from other stars is called galactic cosmic radiation (GCR). Active areas in the galaxy – like supernovae, black holes, and neutron stars – can strip the electrons from atoms and accelerate the nuclei to almost the speed of light, producing GCR.

On Earth, we have three layers of protection from space radiation. The first is the heliosphere, which helps block GCR from reaching the major planets in the solar system. Additionally, Earth’s magnetic field produces a shield called the magnetosphere, which keeps GCR out away from Earth and low-orbiting satellites like the International Space Station. Finally, the gases of Earth’s atmosphere absorb radiation.

When astronauts head to the Moon or to Mars, they won’t have the same protection we have on Earth. They’ll only have the protection of the heliosphere, which fluctuates in size throughout the Sun’s 11-year cycle.

In each solar cycle, the Sun goes through periods of intense activity and powerful solar winds, and quieter periods. Like a balloon, when the wind calms down, the heliosphere deflates. When it picks up, the heliosphere expands.

“The effect the heliosphere has on cosmic rays allows for human exploration missions with longer duration. In a way, it allows humans to reach Mars,” said Arik Posner, a heliophysicist at NASA Headquarters in Washington, D.C. “The challenge for us is to better understand the interaction of cosmic rays with the heliosphere and its boundaries.”

Anatomy of the heliosphere

There is some debate about the precise shape of the heliosphere. However, scientists agree that it has several layers. Let’s look at the layers from inside outward:

This illustration shows the position of NASA’s Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto. Credits: NASA/JPL-Caltech

• Termination shock: All of the major planets in our solar system are located in the heliosphere’s innermost layer. Here, the solar wind emanates out from the Sun at full speed, about a million miles per hour, for billions of miles, unaffected by the pressure from the galaxy. The outer boundary of this core layer is called the termination shock.

• Heliosheath: Beyond the termination shock is the heliosheath. Here, the solar wind moves more slowly and deflects as it faces the pressure of the interstellar medium outside.

• Heliopause: The heliopause marks the sharp, final plasma boundary between the Sun and the rest of the galaxy. Here, the magnetic fields of the solar and interstellar winds push up against each other, and the inside and outside pressures are in balance.

• Outer Heliosheath: The region just beyond the heliopause, which is still influenced by the presence of the heliosphere, is called the outer heliosheath.

How we study the heliosphere’s outer reaches

Many NASA missions study the Sun and the innermost parts of the heliosphere. But only two human-made objects have crossed the boundary of the solar system and entered interstellar space.

In 1977, NASA launched Voyager 1 and Voyager 2. Each spacecraft is equipped with tools to measure the magnetic fields and the particles it is directly passing through. After swinging past the outer planets on a grand tour, they exited the heliopause in 2012 and 2018 respectively and are currently in the outer heliosheath. They discovered that cosmic rays are about three times more intense outside the heliopause than deep inside the heliosphere.

However, the picture the Voyagers paint is incomplete.

“Trying to figure out the entire heliosphere from two points, Voyager 1 and 2, is like trying to determine the weather in the entire Pacific Ocean using two weather stations,” Christian said.

The Voyagers work with the Interstellar Boundary Explorer (IBEX) to study the heliosphere. IBEX is a 176-pound, suitcase-sized satellite launched by NASA in 2008. Since then, IBEX has orbited Earth, equipped with telescopes observing the outer boundary of the heliosphere. IBEX captures and analyzes a class of particle called energetic neutral atoms, or ENAs, that cross its path. ENAs form where the interstellar medium and the solar wind meet. Some ENAs stream back toward the center of the solar system – and IBEX.

“Every time you collect one of those ENAs, you know what direction it came from,” said McComas, IBEX’s principal investigator. “By collecting a lot of those individual atoms, you're able to make this inside out image of our heliosphere.”

In 2025, NASA will launch the Interstellar Mapping and Acceleration Probe (IMAP). IMAP’s ENA cameras are higher resolution and more sensitive than IBEX’s.

Mysteries abound

In 2009, IBEX returned a finding so shocking that researchers initially wondered if the instrument may have malfunctioned. That discovery became known as the IBEX Ribbon – a band across the sky where ENA emissions are two or three times brighter than the rest of the sky.

“The Ribbon was totally unexpected and not anticipated by any theories before we flew the mission,” McComas said. It’s still not entirely clear what causes it, but it is a clear example of the mysteries of the heliosphere that remain to be discovered.

NASA’s Interstellar Boundary Explorer, or IBEX, studies the heliosphere from its orbit around Earth. IBEX’s first-ever skymap showed a surprising feature dubbed the “IBEX ribbon.” Credits: NASA/IBEX

“Our Sun is a star like billions of other stars in the universe. Some of those stars also have astrospheres, like the heliosphere, but this is the only astrosphere we are actually inside of and can study closely,” said Justyna Sokol, a research scientist at Southwest Research Institute in San Antonio, Texas. “We need to start from our neighborhood to learn so much more about the rest of the universe.”

By Alison Gold

NASA's Goddard Space Flight Center, Greenbelt, Md.

Editor: Miles Hatfield

Source: NASA/Sun

---

Dwarf galaxy catches globular cluster

Composite image of NGC 2005 (left) and the Large Magellanic Cloud (right). The chemical composition of the stars in the globular cluster NGC 2005 differs from other stars in the Large Magellanic Cloud. It is the first evidence of merging dwarf galaxies outside our Milky Way. (c) HLA/Fabian RR/ESO/VMC Survey/Astronomie.nl [CC BY-SA 3.0]

Astronomers already knew that our own Milky Way grew by taking in smaller galaxies. But now a team of Italian-Dutch researchers have shown that a small galaxy neighbouring the Milky Way has in turn absorbed an even smaller galaxy from its vicinity. The researchers will publish their findings on Monday in the journal Nature Astronomy.

According to the prevailing theory, large galaxies such as our Milky Way were formed by mergers with smaller galaxies. In recent years, evidence for this has indeed been found for our Milky Way thanks to the Gaia satellite. An Italian-Dutch team of researchers wanted to prove the hypothesis that small galaxies are in turn made up of even smaller ones.

Globular clusters

To test their hypothesis, the researchers studied the Large Magellanic Cloud, a neighbouring galaxy to our Milky Way. They focused in particular at globular clusters. Globular clusters are groups of thousands to millions of stars. The idea is that the core of such a globular cluster can hold out even after billions of years of pushing and pulling in a galaxy.

The researchers analysed the chemical composition of eleven globular clusters collected by the Very Large Telescope and the Magellan telescopes in Chile.

Of the eleven globular clusters studied in the Large Magellanic Cloud, one was found to have a distinctly different chemical composition. It is globular cluster NGC 2005. This cluster contains about 200,000 stars and is located 750 light years away from the centre of the Large Magellanic Cloud. Among other things, it contains less zinc, copper, silicon and calcium than the ten other clusters. 

 

Relic of earlier merger

Based on the chemical composition of NGC 2005, the researchers deduced that the cluster must be a relic of a small galaxy in which the stars formed rather slowly. Billions of years ago, this small galaxy would have merged with the then not so large Large Magellanic Cloud. Over time, most of the small galaxy was pulled apart and most of the stars were scattered, but the central globular cluster NGC 2005, remained.

Researcher Davide Massari, who works in Italy and at the University of Groningen, is delighted: "We are actually seeing a relic of an earlier merger. And we have now convincingly demonstrated for the first time that small galaxies neighboring our Milky Way have in turn built up from even smaller galaxies."

Scientific paper

A relic from a past merger event in the Large Magellanic Cloud. By: A. Mucciarelli, D. Massari, A. Minelli, D. Romano, M. Bellazzini, F.R. Ferraro, F. Matteucci, L. Origlia. In: Nature Astronomy. (preprint, pdf)

Source: Astronomie.nl/Nieuws

---