Stars, supernovae, black holes and stellar remnants

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Astronomers discover the most metal-poor extreme helium star
https://phys.org/news/2024-04-astronome ... elium.html
by Tomasz Nowakowski , Phys.org

Using the Southern African Large Telescope (SALT), astronomers have performed high-resolution observations of a recently detected extreme helium star designated EC 19529–4430. It turned out that EC 19529–4430 is the most metal deficient among the population of known extreme helium stars. The finding was reported in a research paper published April 5 on the pre-print server arXiv.

Extreme helium (EHe) stars are supergiants much larger and hotter than the sun, but less massive. They are almost devoid of hydrogen, which is unusual, as hydrogen is the most abundant chemical element in the universe.

EHes are characterized by relatively sharp and strong lines of neutral helium, which indicates low surface gravities and atmospheres dominated by helium. Besides helium, these stars also have significant amounts of carbon, nitrogen and oxygen. The First EHe star was detected in 1942.

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AI and physics combine to reveal the 3D structure of a flare erupting around a black hole
https://phys.org/news/2024-04-ai-physic ... al-3d.html
by California Institute of Technology

Scientists believe the environment immediately surrounding a black hole is tumultuous, featuring hot magnetized gas that spirals in a disk at tremendous speeds and temperatures. Astronomical observations show that within such a disk, mysterious flares occur up to several times a day, temporarily brightening and then fading away.

Now a team led by Caltech scientists has used telescope data and an artificial intelligence (AI) computer-vision technique to recover the first three-dimensional video showing what such flares could look like around Sagittarius A* (Sgr A*) the supermassive black hole at the heart of our own Milky Way galaxy.

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Pulsating Snake: First millisecond pulsar discovered in the galactic center
https://phys.org/news/2024-04-pulsating ... actic.html
by Tomasz Nowakowski , Phys.org

Astronomers from the Australia Telescope National Facility (ATNF) report the discovery of a new millisecond pulsar in the "Snake"—a radio filament in the galactic center. It is the first millisecond pulsar detected in the center of our galaxy. The finding was detailed in a paper published April 13 on the pre-print server arXiv.

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NASA Releases Time-Lapses of Supernovae Showing 20 Years In 20 Seconds
by Dr Alfredo Carpineti
April 26, 2024

Introduction:

(IFL Science) NASA has released two new movies showcasing changing observations of two well-known sources in the sky: Cassiopeia A and the Crab Nebula. Both headliners are the leftovers of massive stars going supernova in our galaxy. The time-lapse videos condense 20 years of the Chandra X-ray telescope's data into just 20 dramatic seconds.

The explosion that created the Crab Nebula appeared in our sky almost 1,000 years ago in 1054. It was reported by Chinese astronomers and many others across the world (the lack of mentions in Europe might have to do with the Catholic Church). The supernova left behind a pulsar and Chandra has been able to track the very energetic changes around this extreme object from 2000 to 2022.

This is already extraordinary, and even more observations are coming as the jet visible in the 2022 observations will be followed again later this year.
Cassiopeia A is a much younger supernova remnant. It was visible from Earth 340 years ago and Chandra has been observing it since 2000 as well. Previous observations showing its changes focused on the 2000 to 2013 period, but in the new time-lapse this has been extended through 2018. Shockwaves are visible in the observations, where particles are being accelerated, emitting X-rays in the process.

Cassiopeia A has a neutron star in its core, discovered by Chandra shortly after the telescope launched in 1999. The observations were pivotal in helping us to understand better how stars go supernova and how regular neutron stars and pulsars form in that process.

Read more here: https://www.iflscience.com/nasa-releas ... nds-73964

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Black holes observed colliding when universe was only 740m years old

Thu 16 May 2024 15.04 BST

A pair of black holes has been observed colliding in the ancient universe for the first time. The observations, by the James Webb Space Telescope, reveal a merger of two galaxies and the monster black holes at their centres when the universe was just 740m years old, about a 20th of its current age.

The discovery that massive mergers appear to have been common in the infant universe could help explain how supermassive black holes like the one at the heart of the Milky Way achieved such tremendous proportions.

Prof Roberto Maiolino, an astrophysicist at the University of Cambridge, and a member of team behind the observations, said: “One problem that we have in cosmology is explaining how these black holes manage to grow so big. In the past we have always talked about gobbling matter very quickly or being born big. Another possibility is that they grow very fast by merging.”

Until now it was not clear whether the merging of galaxies – which is known to have happened – would also result in the black holes at the centres morphing into a single cosmic sinkhole. Recent models have suggested that one of them would be kicked out into space to become a “wandering black hole”.

The latest observations use the Webb telescope’s ability to get to the far reaches of the cosmos and so have provided the first glimpse of galactic mergers in the distant past.

https://www.theguardian.com/science/art ... ies-merger

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Star Skips Supernova Stage, Collapses Directly Into a Black Hole
The binary star system VFTS 243 could help scientists understand why some stars vanish more suddenly than others.
By Adrianna Nine May 28, 2024
https://www.extremetech.com/science/sta ... black-hole

Most of us are familiar with the term "supernova," or the process by which a star collapses under its own gravity and produces a violent explosion. This stellar event is so luminous that it can light up its galactic neighborhood for several days at a time, offering astronomers a unique opportunity to study the star life cycle and the expansion of the universe. But what happens when a star vanishes without a trace? Following a new study, researchers in Europe believe massive stars might be capable of skipping the supernova stage, instead collapsing directly into a black hole.
Since 2017, scientists have identified more than 800 stars that disappeared one night, never to be seen again. (In some recorded cases, astronomers turned away from looking at a star for just a moment, only to find an empty space where the star had been when they returned.) These so-called "missing stars" challenge the scientific consensus that stars change fairly slowly. And while there's a chance that some of these are variable stars—stars that shine brightly one moment and appear dim the next—it's unlikely that this explains all 800-plus missing objects.

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Eight new millisecond pulsars discovered with FAST

https://phys.org/news/2024-06-milliseco ... -fast.html

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Webb Telescope Spots Oldest Supernova Yet
With a redshift of 2.9, scientists estimate the star exploded when the universe was just 2.3 billion years old.
By Ryan Whitwam June 14, 2024
https://www.extremetech.com/science/web ... ernova-yet

NASA designed the James Webb Space Telescope as the successor to Hubble, but it's not just a sharper version of that observatory. Webb's keen infrared eyes allow it to see ultra-faint objects that existed shortly after the dawn of the universe, a capability researchers leveraged to identify a raft of new (old) supernovae. The team reports Webb's data has revealed 10 times more supernovae in the early universe than previously known.

This work is part of the JWST Advanced Deep Extragalactic Survey (JADES) program, which turns Webb toward vast fields of ancient galaxies. As the universe expands, light is stretched into longer wavelengths. This "redshift" is most extreme for the oldest and most distant objects, which can have a redshift of 2 or more, which indicates they existed when the universe was no more than 3.3 billion years old.

Identifying these objects wasn't as simple as pointing Webb at the sky and capturing an image. Webb observed this patch of sky in two observational campaigns separated by a year, which allowed the team to look for objects that show varying brightness. These transient signals are mostly supernovae that behave like the exploding stars we see all over the modern universe.

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High-speed baby stars circle the supermassive black hole Sgr A* like a swarm of bees
https://phys.org/news/2024-06-high-baby ... ssive.html
by University of Cologne

Observational astronomy shows that newly discovered young stellar objects (YSOs) in the immediate vicinity of the supermassive black hole Sagittarius A* located in the center of our galaxy behave differently than expected. They describe similar orbits to already known young evolved stars and are arranged in a particular pattern around the supermassive black hole.

Studies show that Sgr A* causes the stellar objects to adopt certain formations. The study is titled "Candidate young stellar objects in the S-cluster: Kinematic analysis of a subpopulation of the low-mass G objects close to Sgr A*" and has been published in Astronomy & Astrophysics.

It involved researchers from the University of Cologne, Masaryk University in Brno (Czech Republic), Charles University in Prague (Czech Republic), the Academy of Sciences of the Czech Republic and the Max Planck Institute for Radio Astronomy in Bonn.

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A black hole of inexplicable mass: JWST observations reveal a mature quasar at cosmic dawn
https://phys.org/news/2024-06-black-hol ... -jwst.html
by Max Planck Society

The James Webb Space Telescope observed a galaxy in a particularly young stage of the universe. Looking back into the past, it became clear that the light from the galaxy called J1120+0641 took almost as long to reach Earth as the universe has taken to develop to the present day. It is inexplicable how the black hole at its center could have weighed over a billion solar masses back then, as independent measurements have shown. The findings are published in the journal Nature Astronomy.

Recent observations of the material in close vicinity to the black hole were supposed to reveal a particularly efficient feeding mechanism, but they found nothing particular. This result is all the more extraordinary: it could mean that astrophysicists understand less about the development of galaxies than they thought. And yet they are by no means disappointing.

The first billion years of cosmic history pose a challenge: The earliest known black holes in the centers of galaxies have surprisingly large masses. How did they get so massive, so quickly? The new observations described here provide strong evidence against some proposed explanations, notably against an "ultra-effective feeding mode" for the earliest black holes.

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Nearest millisecond pulsar has radius of 11.4 kilometers and is 1.4x as heavy as the sun, researchers find
https://phys.org/news/2024-07-nearest-m ... eters.html
by Netherlands Research School for Astronomy

The nearest millisecond pulsar PSR J0437-4715 has a radius of 11.4 kilometers and a mass 1.4 times that of the sun. These are the results of precision measurements made by a team of researchers led by the University of Amsterdam (the Netherlands). The measurements reveal more about the composition and magnetic field of this neutron star. The researchers are publishing their findings in a series of scientific papers.

PSR J0437 is a pulsar, a rotating neutron star that emits electromagnetic radiation. It is located about 510 light-years from Earth in the southern constellation of Pictor. PSR J0437 rotates 174 times per second around its axis and has a white dwarf companion.

Like an out of control lighthouse, the pulsar sends a beam of radio waves and X-rays toward Earth every 5.75 milliseconds. This makes it the closest millisecond pulsar to Earth. It is also, in part because it is so close, the brightest millisecond pulsar. And it is a more stable clock than man-made atomic clocks.

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Event Horizon Telescope makes highest-resolution black hole detections from Earth
https://phys.org/news/2024-08-event-hor ... ution.html
by Center for Astrophysics | Harvard & Smithsonian

The Event Horizon Telescope (EHT) Collaboration has conducted test observations achieving the highest resolution ever obtained from the surface of the Earth, by detecting light from the centers of distant galaxies at a frequency of around 345 GHz.

When combined with existing images of supermassive black holes at the hearts of M87 and Sgr A at the lower frequency of 230 GHz, these new results will not only make black hole photographs 50% crisper but also produce multi-color views of the region immediately outside the boundary of these cosmic beasts.

The new detections, led by scientists from the Center for Astrophysics | Harvard & Smithsonian (CfA) that includes the Smithsonian Astrophysical Observatory (SAO), are published in The Astronomical Journal.

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Dark Matter Could Have Helped Make Supermassive Black Holes in the Early Universe
August 28, 2024

Introduction:

(Eurekalert) Key takeaways

• Supermassive black holes typically take billions of years to form. But the James Webb Space Telescope is finding them not that long after the Big Bang — before they should have had time to form.

• UCLA astrophysicists have discovered that if dark matter decays, the photons it emits keep the hydrogen gas hot enough for gravity to gather it into giant clouds and eventually condense it into a supermassive black hole.

• In addition to explaining the existence of very early supermassive black holes, the finding lends support for the existence of a kind of dark matter capable of decaying into particles such as photons.

It takes a long time for supermassive black holes, like the one at the center of our Milky Way galaxy, to form. Typically, the birth of a black hole requires a giant star with the mass of at least 50 of our suns to burn out – a process that can take a billion years – and its core to collapse in on itself.
Even so, at only about 10 solar masses, the resulting black hole is a far cry from the 4 million-solar-masses black hole, Sagittarius A*, found in our Milky Way galaxy, or the billion-solar-mass supermassive black holes found in other galaxies. Such gigantic black holes can form from smaller black holes by accretion of gas and stars, and by mergers with other black holes, which take billions of years.

Why, then, is the James Webb Space Telescope discovering supermassive black holes near the beginning of time itself, eons before they should have been able to form? UCLA astrophysicists have an answer as mysterious as the black holes themselves: Dark matter kept hydrogen from cooling long enough for gravity to condense it into clouds big and dense enough to turn into black holes instead of stars.

Read more here: https://www.eurekalert.org/news-releases/1056016

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Small Black Holes Couldn’t Have Existed After the Big Bang – Or They Would Have Destroyed the Universe
by Dr. Alfredo Carpineti
September 9, 2024

Introduction:

(IFL Science) For several decades, scientists have toyed with the idea of primordial black holes. In the smorgasbord of particles and forces and energy of the beginning, slight overdensities might have led to the formation of small black holes. But not too small. Because under a certain limit, these objects would have wiped out the universe already.

This might appear counterintuitive if you imagine black holes are unstoppable devourers of matter. But black holes are mostly chill as long as you stay away from them. So how do these extreme objects cause the end of the universe? They might mess with the Higgs Boson. Scientists have now worked out a connection between the two and luckily got the reassurance of why we are still here.

The Higgs boson is the particle that gives everything in the universe mass. Mass as we know it is an interaction between the particles that make us, for example, and the Higgs field. We have proven its existence for just over a decade and current understanding suggests that it's in a metastable state. Potentially, its energy could be lower and that is a problem.

“If [the Higgs field] would suddenly change its properties then light particles could become potentially heavy or the other way around, and then physics forces, matter, masses will all change, and then the world around us would not be the same anymore. We might not even be there anymore to actually see it because we might just completely fall apart,” Dr Lucien Heurtier, from King’s College London, told IFLScience.

It is likely that this change would destroy the universe as we know it in a process called vacuum decay: a bubble of true vacuum – where the lowest possible energy for the Higgs exists – will expand and destroy the universe. Yes, that is definitely bad news, but there is also good news.

The article goes on to note that the Higgs field is apparently very stable, so we don’t have to worry about the consequences of a sudden change in its properties.

Read more of the IFL Science article here: https://www.iflscience.com/small-black ... se-75878

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