Unusual stars detected.

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Message 2086670 - Posted: 22 Oct 2021, 20:44:16 UTC

Weird stellar remnant may be from one of the first stars in the universe.

Astronomers have detected an extremely unusual star that they believe is a stellar fossil, or remnant, of one of the universe's very first stars.

The star, named AS0039, is located in the Sculptor dwarf galaxy around 290,000 light-years from the solar system. This stellar remnant has the lowest concentration of metal, particularly iron, of any star measured outside the Milky Way. The researchers think that finding is evidence that the remnant is a direct descendent of one of the universe's earliest stars, which contained very little metal.
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Message 2086674 - Posted: 22 Oct 2021, 20:51:22 UTC
Last modified: 22 Oct 2021, 20:51:36 UTC

Strange white dwarf switches 'on' and 'off' in front of astronomers.

A spacecraft that usually seeks new worlds saw a white dwarf suddenly switch "off" with a swift drop in brightness. Then it switched back on again.

This observation represents the first time astronomers saw a white dwarf change its luminosity, or inherent brightness, so quickly, and may have implications for how we understand the process of accretion (or building up material) at many types of celestial objects.

White dwarfs are the remnants of much larger stars approximately the size of our sun that have burned off all the hydrogen that previously fueled them. As such, sometimes astronomers say that looking at white dwarf systems helps us learn about our own solar system's distant future, when the sun runs out of hydrogen in about 5 billion years.

The new star research was conducted using NASA's Transiting Exoplanet Survey Satellite (TESS), whose main mission is to seek Earth-size worlds relatively close to our own planet, on a larger quest to understand how prolific life may be in the universe. In this case, TESS spotted the fluctuating brightness at a star called TW Pictoris, which is roughly 1,400 light-years from Earth.

The luminosity changes took place because the white dwarf is pulling off material from a nearby companion star, in a process known as accretion. As the white dwarf "feeds" off its companion, it grows brighter.

The white dwarf lost luminosity in only 30 minutes, much faster than other white dwarfs that have faded over several days or months. Why is still unknown, as the flow of material on to the white dwarf's accretion disc should be constant, but astronomers suspect it might be due to fluctuations in the dwarf's magnetic field.
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Message 2089059 - Posted: 26 Nov 2021, 20:26:32 UTC

The Hottest White Dwarf We Know of Is Up to Something Ghoulish With Its Neighbor.

There's a dead star behaving very oddly 1,300 light-years away.

It's a white dwarf named KPD 0005+5106, and X-ray data from the Chandra space telescope have revealed that it's enacting extreme violence on an orbiting companion. Not only is it siphoning material from this object (which, to be fair, is pretty normal for white dwarfs), the star is giving its companion an absolute drubbing by blasting it with radiation from close proximity.

Even more interestingly, we can't see what the companion actually is, making it tricky to predict its eventual fate, including how long it will take to be completely destroyed and what that will mean for the white dwarf.

"We didn't know this white dwarf had a companion before we saw the X-ray data," said astronomer You-Hua Chu of the Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA) in Taiwan. "We've looked for the companion with optical light telescopes but haven't seen anything, which means it is a very dim star, a brown dwarf, or a planet."

White dwarfs are what happens to a star under about eight times the mass of the Sun once it runs out of elements it can fuse in its core. As the fuel runs low, it will eject its outer layers into space until finally, the core is no longer able to support itself and collapses under its own gravity into a dense object about the size of Earth (and sometimes even smaller).

Although it may be without fuel to fuse, the white dwarf remains extremely hot, so hot that it will continue to shine brightly with thermal radiation for billions of years. The average white dwarf will have a temperature of over 100,000 Kelvin (99,727 degrees Celsius or 179,540 degrees Fahrenheit) once its core stops contracting. The Sun, for context, has an effective temperature of 5,772 Kelvin......
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Message 2089739 - Posted: 7 Dec 2021, 8:20:14 UTC

Scientists Said These Stars Were Too Small to Exist, But We Finally Know Their Secret.

Astronomers have finally observed the satisfying solution to a perplexing cosmic problem: the apparent mystery of stars that are basically too small to exist.

White dwarfs that are considered to be too tiny to exist in the current lifetime of the Universe have now, however, been spotted having their mass slurped off by binary companions – a mechanism long suspected that might explain their size, but never before proven in the wild.

These 'missing link' binaries are called evolved cataclysmic variables, and their discovery helps us understand one of the stages on the evolutionary path of dead stars.

"We have observed the first physical proof of a new population of transitional binary stars," says astronomer Kareem El-Badry of the Harvard & Smithsonian Center for Astrophysics.

"This is exciting; it's a missing evolutionary link in binary star formation models that we've been looking for."

White dwarfs are what becomes of a star less than about eight times the mass of the Sun when it runs out of fuel for the process of nuclear fusion.

The dying star ejects most of its mass, and the core collapses down into an extremely dense object – up to about 1.4 times the mass of the Sun, packed into a sphere around the size of Earth (although they can vary).

On rare occasions, however, they can be so low in mass that, according to our models of stellar evolution, they shouldn't exist. These extremely low-mass white dwarfs, or ELMs, are only around one-third of the mass of the Sun. Such mass loss should take far longer than the current lifetime of the Universe, which is only around 13.8 billion years.....

...."We found the evolutionary link between two classes of binary stars – cataclysmic variables and ELM white dwarfs – and we found a decent number of them."

Most of the binaries consisted of a white dwarf around 0.15 times the mass of the Sun, with companions around 0.8 times the mass of the Sun.

All of the white dwarfs showed signs of mass loss to their companion stars; for 13 of the stars, the process was still ongoing, while the remaining eight were no longer losing mass, but were puffy, as though mass loss was recent. All 21 of the stars were hotter and brighter than usually seen in a cataclysmic variable white dwarf.

More work is needed in order to fully understand the population of evolved cataclysmic variables, including more detailed observations of the 21 binaries. The team also hopes to go back and take a closer look at the other 29 binaries from the initial 50 candidates.
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Message 2101391 - Posted: 15 Jun 2022, 22:23:23 UTC

Fastest nova ever recorded burns out in just one day.

The fastest nova star explosion ever seen has been recorded by astronomers.

They watched as a white dwarf star 'stole' gas from a nearby red giant and triggered a blast bright enough to be witnessed from Earth with binoculars.

Named V1674 Hercules, the nova explosion occurred 100 light-years away on June 12 last year but lasted for just a day — up to three times quicker than any previously observed.

A nova is a sudden explosion of bright light from a two-star system. Every nova is created by a white dwarf – the very dense leftover core of a star – and a nearby companion star.

Experts from Arizona State University hope their observation will help answer larger questions about the chemistry of our solar system, the death of stars and the evolution of the universe...
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Message 2102164 - Posted: 28 Jun 2022, 20:29:18 UTC

Meet the 'zombie star' that survived a supernova blast.

Astronomers have observed in a relatively nearby galaxy a star that not only survived what ordinarily should have been certain death - a stellar explosion called a supernova - but emerged from it brighter than before the blast.

Meet the "zombie star."

The star at issue, observed with the Hubble Space Telescope, is a kind known as a white dwarf, an incredibly dense object with about the mass of the sun crammed into the size of Earth. A white dwarf is the remaining core of a star that blew off a lot of its material at the end of its life cycle, as our sun is expected to do about 5 billion years from now.

This white dwarf is gravitationally locked in orbit with another star - a pairing called a binary system - and with its strong gravitational pull siphoned off and incorporated a good deal of material from this unfortunate companion.

That is where the trouble started. In doing so, the white dwarf reached a mass threshold - about 1.4 times that of the sun - that caused thermonuclear reactions in its core that made it detonate in a supernova, an event that should have killed it....
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Message 2104370 - Posted: 3 Aug 2022, 7:28:31 UTC

How much can a neutron star take before it collapses into a black hole?

Gluttonous cosmic 'black widow' is heaviest-known neutron star.

Astronomers have observed the most massive known example of an object called a neutron star, one classified as a "black widow" that got particularly hefty by gobbling up most of the mass of a stellar companion trapped in an unhappy cosmic marriage.

The researchers said the neutron star, wildly spinning at 707 times per second, has a mass about 2.35 times greater than that of our sun, putting it perhaps at the maximum possible mass for such objects before they would collapse to form a black hole.

A neutron star is the compact collapsed core of a massive star that exploded as a supernova at the end of its life cycle. The one described by the researchers is a highly magnetized type of neutron star called a pulsar that unleashes beams of electromagnetic radiation from its poles. As it spins, these beams appear from the perspective of an observer on Earth to pulse - akin to a lighthouse's rotating light.

Only one other neutron star is known to spin more quickly than this one....
I guess that we'll eventually find out.

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Message 2105024 - Posted: 13 Aug 2022, 0:27:40 UTC

It is still defying explanation.

Supergiant Star Betelgeuse Blew Its Top in a Violent Explosion, Baffling Scientists.

When the bright, red supergiant star Betelgeuse blew its top in 2019, the Hubble Space Telescope and other observatories were there to see it. Through this surface mass ejection, Betelgeuse offloaded 400 billion times as much mass as the sun does during a typical coronal mass ejection, a regular event in which the sun casts off part of its outer atmosphere, called the corona.

This wasn’t some sort of supernovae finale event, though. Betelgeuse—one of the most prominent stars in the Milky Way, a part of the Orion constellation—still seemingly acts like a normal star, and may even be recovering. After analyzing the 2019 data, astronomers have concluded that this is behavior we’ve never seen before in a normal star....
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Message 2109902 - Posted: 9 Nov 2022, 20:17:24 UTC

Bang!

Supernova explosion that ripped star apart 11.5 billion years ago detected by Hubble telescope.

Around 11.5 billion years ago, a giant red star collapsed and exploded, creating a spectacular supernova in the early universe.

Light from the star's cataclysmic death made its way through space and time to eventually be captured by the Hubble Space Telescope in 2010.

But it was not discovered until a team of scientists, led by Wenlei Chen of the University of Minnesota, trawled through Hubble's archives.

"This could be the earliest core-collapse supernova [yet discovered]," Dr Chen said.

Hubble caught the moments just after the star exploded in a series of three images, the team reports today in the journal Nature...

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Message 2110419 - Posted: 20 Nov 2022, 21:06:58 UTC

Colliding Neutron Stars Created a Neutron Star We Thought Too Heavy to Exist.

A flash of light emitted by colliding neutron stars has once again upended our understanding of how the Universe works.

Analysis of the short gamma-ray burst spat out as the two stars merged revealed that, rather than forming a black hole, as expected, the immediate product of the merger was a highly magnetized neutron star far heavier than the estimated maximum neutron star mass.

This magnetar seems to have persisted for over a day before collapsing down into a black hole.

"Such a massive neutron star with a long life expectancy is not normally thought to be possible," astronomer Nuria Jordana-Mitjans of the University of Bath in the UK told The Guardian. "It is a mystery why this one was so long-lived."...
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Message boards : Science (non-SETI) : Unusual stars detected.


 
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