Stars, supernovae, black holes and stellar remnants

weatheriscool
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Webb telescope finds brown dwarf with dust clouds in its atmosphere
https://phys.org/news/2022-09-webb-tele ... louds.html
by Bob Yirka , Phys.org

The James Webb Space Telescope (JWST) captured images of a brown dwarf with silicate particles in its atmosphere. In their paper posted on the arXiv preprint server, astronomers describe their analysis of the brown dwarf and its unique atmosphere.

Brown dwarfs are space objects that some have dubbed failed stars. They begin their existence in much the same way as other stars but fail to build up enough hydrogen to instigate a fusion reaction. Because of that, they do not grow to the size of stars; hence, their name. Brown dwarfs are able to fuse deuterium, though the temperature and pressure are much lower than hydrogen in stars. They also emit heat and light, which is why space scientists are able to see them, generally by studying infrared wavelengths. And it just so happens that studying objects in the infrared spectrum is what the JWST was designed to do.

The brown dwarf observed by the researchers is approximately 72 light years away—it was first observed in 2015 and is named VHS 1256-1257 b. Its size is roughly 19 times that of Jupiter and previous research has shown that it is still young. Prior images of the dwarf have shown that it has a reddish hue to its atmosphere, which is what caught the attention of the researchers.
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Re: Stars, supernovae, black holes and stellar remnants

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A first glimpse at the high-productivity star factory in the galactic center
https://phys.org/news/2022-09-glimpse-h ... actic.html
by Max Planck Society
With the help of detailed observations, astronomers have managed to get a first representative glimpse of the numerous young stars in the central regions of our home galaxy. The observations provide evidence for star formation in the galactic center having started off near the center and then worked its way outwards. This confirms a mode of star formation that had earlier been found in the centers of other, distant galaxies. The results also reveal that most stars in that region did not form in tightly-bound massive clusters, but in loose associations whose member stars have long since gone their separate ways. The results have been published in Nature Astronomy.

When it comes to stars, the central region of our home galaxy, the Milky Way, is considerably more crowded than other parts of our galaxy. Astronomers have long been hoping this might provide them with a laboratory for studying rapid star formation—a phenomenon that occurs in numerous other galaxies, and in particular during the earliest billions of years of cosmic history. But the crowding makes stars in the central region notoriously difficult to observe.

Now, a new analysis based on a high-resolution infrared survey, which has just been published in Nature Astronomy, provides a first representative reconstruction of star formation history in the galactic central region. It also shows that most young stars in the galactic center formed not in tightly-knit massive clusters, but in loose stellar association, which dispersed over the past millions of years.
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Re: Stars, supernovae, black holes and stellar remnants

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Astronomers discover new brown dwarf with quasi-spherical mass loss
https://phys.org/news/2022-09-astronome ... -mass.html
by Tomasz Nowakowski , Phys.org

Astronomers report the detection of a new brown dwarf as part of the Ophiuchus Disk Survey Employing ALMA (ODISEA) program. The newfound object, designated SSTc2d J163134.1-24006, appears to be experiencing a quasi-spherical mass loss. The discovery was detailed in a paper published September 2 on the arXiv pre-print repository.

Brown dwarfs are intermediate objects between planets and stars, occupying the mass range between 13 and 80 Jupiter masses (0.012 and 0.076 solar masses). They can burn deuterium but are unable to burn regular hydrogen, which requires a minimum mass of at least 80 Jupiter masses and a core temperature of about 3 million K.

A team of astronomers led by Dary Ruiz-Rodriguez of the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, have investigated SSTc2d J163134.1-24006, initially identified as a faint stellar object, under the ODISEA project, which is dedicated to study the entire population of protoplanetary disks in the Ophiuchus Molecular Cloud. They found that SSTc2d J163134.1-24006 is most likely a brown dwarf with a mass of about 0.05 solar masses, and an elliptical shell of carbon monoxide (CO).
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Re: Stars, supernovae, black holes and stellar remnants

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Astrophysics: Stars' childhoods shape stellar evolution
https://phys.org/news/2022-09-astrophys ... ution.html
by University of Innsbruck
In classical models of stellar evolution, so far little importance has been attached to the early evolution of stars. Thomas Steindl from the Department of Astro- and Particle Physics at the University of Innsbruck now shows for the first time that the biography of stars is indeed shaped by their early stage. The study was published in Nature Communications.

From babies to teenagers, stars in their "young years" are a major challenge for science. The process of star formation is particularly complex and difficult to map in theoretical models. One of the few ways to learn more about the formation, structure or age of stars is to observe their oscillations. "Comparable to the exploration of the Earth's interior with the help of seismology, we can also make statements about their internal structure and thus also about the age of stars based on their oscillations," says Konstanze Zwintz.

The astronomer is regarded as a pioneer in the young field of asteroseismology and heads the research group Stellar Evolution and Asteroseismology at the Institute for Astro- and Particle Physics at the University of Innsbruck. The study of stellar oscillations has evolved significantly in recent years because the possibilities for precise observation through telescopes in space such as TESS, Kepler, and James Webb have improved on many levels. These advances are now also shedding new light on decades-old theories of stellar evolution.
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Re: Stars, supernovae, black holes and stellar remnants

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The Orbit of a Sun-Like Star Reveals the Nearest Black Hole Ever Found
by Matt Williams
September 20, 2022

Introduction:
(Science Alert) In 1916, Karl Schwarzchild theorized the existence of black holes as a resolution to Einstein's field equations for his Theory of General Relativity.

By the mid-20th century, astronomers began detecting black holes for the first time using indirect methods, which consisted of observing their effects on surrounding objects and space.

Since the 1980s, scientists have studied supermassive black holes (SMBHs), which reside at the center of most massive galaxies in the Universe. And by April 2019, the Event Horizon Telescope (EHT) collaboration released the first image ever taken of an SMBH.

These observations are an opportunity to test the laws of physics under the most extreme conditions and offer insights into the forces that shaped the Universe.

According to a recent study, an international research team relied on data from the ESA's Gaia Observatory to observe a Sun-like star with strange orbital characteristics. Due to the nature of its orbit, the team concluded that it must be part of a black hole binary system.

This makes it the nearest black hole to our Solar System and implies the existence of a sizable population of dormant black holes in our galaxy.
Read more here: https://www.sciencealert.com/the-orbit ... er-found
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Re: Stars, supernovae, black holes and stellar remnants

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Blob of hot gas swirls around Milky Way black hole at 30% speed of light

Thursday, September 22, 2022

Astronomers further constrain the shape of the magnetic field of the Milky Way's supermassive black hole, Sagittarius A*.

https://astronomy.com/news/2022/09/milk ... -hole-blob


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Re: Stars, supernovae, black holes and stellar remnants

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A New FRB Signal Has Buzzed Nearly 2,000 Times in Just Two Months, Raising a Mystery
by Michele Starr
September 24, 2022

Introduction:
(Science Alert) We have detected a strange new signal from across the chasm of time and space.

A repeating fast radio burst source detected last year was recorded spitting out a whopping 1,863 bursts over 82 hours, amid a total of 91 hours of observation.

This hyperactive behavior has allowed scientists to characterize not just the galaxy that hosts the source and its distance from us, but also what the source is.

The object, named FRB 20201124A, was detected with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China and described in a new paper led by astronomer Heng Xu of Peking University in China.

So far most evidence points to a magnetar – a neutron star with extraordinarily strong magnetic fields – as a source of FRB emissions like this.
Read more here: https://www.sciencealert.com/a-new-frb ... a-mystery
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Re: Stars, supernovae, black holes and stellar remnants

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Potential first traces of the universe's earliest stars
https://phys.org/news/2022-09-potential ... stars.html
by National Science Foundation
The very first stars likely formed when the universe was only 100 million years old, less than one percent its current age. These first stars—known as Population III—were so titanically massive that when they ended their lives as supernovae they tore themselves apart, seeding interstellar space with a distinctive blend of heavy elements. Despite decades of diligent searching by astronomers, however, there has been no direct evidence of these primordial stars, until now.

By analyzing one of the most distant known quasars using the Gemini North telescope, one of the two identical telescopes that make up the International Gemini Observatory, operated by NSF's NOIRLab, astronomers now think they have identified the remnant material of the explosion of a first-generation star. Using an innovative method to deduce the chemical elements contained in the clouds surrounding the quasar, they noticed a highly unusual composition—the material contained over 10 times more iron than magnesium compared to the ratio of these elements found in our sun.

The scientists believe that the most likely explanation for this striking feature is that the material was left behind by a first-generation star that exploded as a pair-instability supernova. These remarkably powerful versions of supernova explosions have never been witnessed, but are theorized to be the end of life for gigantic stars with masses between 150 and 250 times that of the sun.
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Re: Stars, supernovae, black holes and stellar remnants

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Speeding Cloud Might Come From Recent, Nearby Supernova
by Govert Schilling
October 7, 2022

Introduction:
(Sky & Telescope)) A mysterious cloud of neutral hydrogen gas, once thought to be falling fast into the Milky Way from its outskirts, might instead be the product of a recent, nearby supernova.

According to solar physicist Joan Schmelz (USRA) and her husband and collaborator, radio astronomer Gerrit Verschuur, the stellar explosion took place some 100,000 years ago, around the time Homo sapiens left Africa and migrated into Asia and Europe.

High-velocity clouds (HVCs) are generally thought to be huge, massive, and many thousands of light-years away. But because there’s no good way of measuring their distance, their origin is still unclear. Most astronomers believe they have been blown out of the Milky Way by a process known as a galactic fountain. Alternatively, they could be intergalactic clouds of primordial gas falling prey to our galaxy’s gravity.

However, a radio-bright HVC known as MI, which is speeding towards us at 120 kilometers per second (268,000 mph), may be much closer – and thus much smaller and less massive — than previously thought. In a study to appear in The Astrophysical Journal (arXiv preprint available here: https://arxiv.org/ftp/arxiv/papers/2207/2207.08707.pdf), Schmelz and Verschuur argue that it was ejected by a dying star, and subsequently accelerated when that star went supernova.

The couple’s interest was piqued when they discovered that MI’s sky position, in Ursa Major, coincides with an 80-light-year-wide spherical bubble in the Milky Way’s interstellar medium. A supernova might have carved out this cavity, and now Schmelz and Verschuur think they have identified the blast’s remnant: the invisible companion of the naked-eye star 56 Ursae Majoris, which sits a few degrees south of the Big Dipper’s bowl.


Read more here: https://skyandtelescope.org/astronomy- ... upernova/
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Re: Stars, supernovae, black holes and stellar remnants

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I actually did not read the entire article cited below. I have watched discussions about so-called "vampire stars' on How the Universe Works featured on the Science Channel. Fascinating stuff.

A Vampire Star And Its Victim Have Been Found in The Tightest Embrace Yet
Evan Gough
October 12, 2022

Introduction:
(Science Alert) We don't have to worry too much about our Sun. It can burn our skin, and it can emit potent doses of charged material – called solar storms – that can damage electrical systems. But the Sun is alone up there, making things simpler and more predictable.

Other stars are locked in relationships with one another as binary pairs. A new study found a binary pair of stars that are so close to each other they orbit every 51 minutes, the shortest orbit ever seen in a binary system. Their proximity to one another spells trouble.

Stars this close to each other are called cataclysmic variables. In cataclysmic variables, the primary star is a white dwarf; in this pair, the other star is a Sun-like star, but older.

White dwarfs are tiny for stars, about the size of the Earth, but they're incredibly dense. The white dwarf's powerful gravity draws material away from its companion, the donor star. The material forms an accretion ring around the white dwarf. This process creates bright flashes at irregular or variable times as the disk heats and material falls into the white dwarf.

The stars in a cataclysmic variable (CV) must be close together for the white dwarf "vampire star" to draw material from the donor star.
Read more here: https://www.sciencealert.com/a-vampire ... brace-yet
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