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