Stars, supernovae, black holes and stellar remnants

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Re: Stars, supernovae, black holes and stellar remnants

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Exploring how stars determine their own masses
https://phys.org/news/2022-08-exploring ... asses.html
by Northwestern University
Last year, a team of astrophysicists including key members from Northwestern University launched STARFORGE, a project that produces the most realistic, highest-resolution 3D simulations of star formation to date. Now, the scientists have used the highly detailed simulations to uncover what determines the masses of stars, a mystery that has captivated astrophysicists for decades.

In a new study, the team discovered that star formation is a self-regulatory process. In other words, stars themselves set their own masses. This helps explain why stars formed in disparate environments still have similar masses. The new finding may enable researchers to better understand star formation within our own Milky Way and other galaxies.

The study was published last week in the Monthly Notices of the Royal Astronomical Society. The collaborative team included experts from Northwestern, University of Texas at Austin (UT Austin), Carnegie Observatories, Harvard University and the California Institute of Technology. The lead author of the new study is Dávid Guszejnov, a postdoctoral fellow at UT Austin.
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Re: Stars, supernovae, black holes and stellar remnants

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Brightest stars in the night sky can strip Neptune-sized planets to their rocky cores
https://phys.org/news/2022-08-brightest ... sized.html
by Robert Sanders, University of California - Berkeley
Over the last 25 years, astronomers have found thousands of exoplanets around stars in our galaxy, but more than 99% of them orbit smaller stars—from red dwarfs to stars slightly more massive than our sun, which is considered an average-sized star.

Few have been discovered around even more massive stars, such as A-type stars—bright blue stars twice as large as the sun—and most of the exoplanets that have been observed are the size of Jupiter or larger. Some of the brightest stars in the night sky, such as Sirius and Vega, are A-type stars.

University of California, Berkeley, astronomers now report a new, Neptune-sized planet—called HD 56414 b—around one of these hot-burning, but short-lived, A-type stars and provide a hint about why so few gas giants smaller than Jupiter have been seen around the brightest 1% of stars in our galaxy.

Current exoplanet detection methods most easily find planets with short, rapid orbital periods around their stars, but this newly found planet has a longer orbital period than most discovered to date. The researchers suggest that an easier-to-find Neptune-sized planet sitting closer to a bright A-type star would be rapidly stripped of its gas by the harsh stellar radiation and reduced to an undetectable core.
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Re: Stars, supernovae, black holes and stellar remnants

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Astronomers detect new eclipsing post-common-envelope binary
https://phys.org/news/2022-08-astronome ... inary.html
by Tomasz Nowakowski , Phys.org
Astronomers have conducted photometric and spectroscopic observations of a binary system known as TIC 60040774. Results of the observational campaign shed more light on the properties of this system, revealing that it is an eclipsing post-common-envelope binary. The study was published August 5 on arXiv.org.

A common envelope (CE) is gas that contains a binary star system. Observations show that once the more massive star in a binary leaves the main sequence, and depending on the initial conditions, dynamically unstable mass transfer or a tidal instability may force such a system to enter the CE phase.

The CE evolution produces a significant population of close, but detached white-dwarf/main-sequence (WDMS) binaries. Approximately a quarter of WDMS are close enough that they must be the so-called post-common-envelope binaries (PCEBs), and about 10% of these systems exhibit eclipses. Studies of PCEBs could advance our knowledge regarding formation and evolution of close compact binary stars.

That is why a team of astronomers led by Rhorom Priyatikanto of the National Research and Innovation Agency in Bandung, Indonesia, investigated TIC 60040774—one of the close binaries with a low-mass secondary star, located some 437 light years away. Previous studies have suggested that it may be a PCEB.
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Re: Stars, supernovae, black holes and stellar remnants

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Astronomers discover new accreting millisecond X-ray pulsar
https://phys.org/news/2022-08-astronome ... ulsar.html
by Tomasz Nowakowski , Phys.org
Using the Neutron Star Interior Composition Explorer (NICER), an international team of astronomers have detected a new accreting millisecond X-ray pulsar. The newfound pulsar, designated MAXI J1816–195, has a spin period of about 1.89 milliseconds. The finding is reported in a paper published August 9 on the arXiv pre-print repository.

X-ray pulsars exhibit strict periodic variations in X-ray intensity, which can be as short as a fraction of a second. Accreting millisecond X-ray pulsars (AMXPs) are a peculiar type of X-ray pulsars in which short spin periods are caused by long-lasting mass transfer from a low-mass companion star through an accretion disk onto a slow-rotating neutron star. Astronomers perceive AMXPs as astrophysical laboratories that could be crucial in advancing our knowledge about thermonuclear burst processes.

AMXPs are relatively rare and to date only a few dozen objects of this type have been identified. In order to expand the list of these peculiar objects, the scientific community is still actively searching for such sources using space observatories like NICER installed on the International Space Station (ISS).
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Re: Stars, supernovae, black holes and stellar remnants

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Astronomers Have Discovered a Black Hole Jet That Is 50 Times Larger Than Its Galaxy
20 August 2022

Image

Astronomers at Western Sydney University have discovered one of the biggest black hole jets in the sky.

Spanning more than a million light years from end to end, the jet shoots away from a black hole with enormous energy, and at almost the speed of light. But in the vast expanses of space between galaxies, it doesn't always get its own way.

At a mere 93 million light-years away, the galaxy NGC2663 is in our neighborhood, cosmically speaking. If our galaxy were a house, NGC2663 would be a suburb or two away.

Looking at its starlight with an ordinary telescope, we see the familiar oval shape of a "typical" elliptical galaxy, with about ten times as many stars as our own Milky Way.

Typical, that is, until we observed NGC2663 with CSIRO's Australian Square Kilometre Array Pathfinder (ASKAP) in Western Australia – a network of 36 linked radio dishes forming a single super-telescope.
https://www.sciencealert.com/astronomer ... its-galaxy
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Re: Stars, supernovae, black holes and stellar remnants

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Researchers detect dozens of new variable stars
https://phys.org/news/2022-08-dozens-va ... stars.html
by Tomasz Nowakowski , Phys.org

By observing the field of globular cluster Palomar 2 with the Indian Astronomical Observatory (IAO), astronomers have discovered 32 new variable stars. The newfound variables are mostly RR Lyrae stars and cluster members. The finding is reported in a paper published August 16 on the arXiv pre-print repository.

Variable stars could offer important hints into aspects of stellar structure and evolution. They could also help us better understand the distance scale of the universe. In particular, the so-called RR Lyrae (RRL) variables are a powerful tool for studying the morphology, metallicity and age of galaxies, especially those with low surface brightness. In general, RRLs are pulsating horizontal branch stars of spectral class A or F, with a mass of around half the sun's.

Now, a team of astronomers led by Armando Arellano Ferro of the National Autonomous University of Mexico (UNAM) reports the detection of dozens of new variables. The discovery is a result of long-term observations of the field of Palomar 2 with IAO's 2.0-m telescope. Palomar 2 is a distant globular cluster located some 100,000 light years in the constellation of Auriga and so far no variables have been reported in this stellar grouping.

"A CCD VI imaging time-series over 11-year is employed to explore the light curves of stars in the field of Palomar 2.... The data were obtained between December 12, 2010 and February 12, 2021 with the 2.0-m telescope at the Indian Astronomical Observatory (IAO), Hanle, India," the researchers wrote in the paper.
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Re: Stars, supernovae, black holes and stellar remnants

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ALMA witnesses deadly star-slinging tug-of-war between merging galaxies
https://phys.org/news/2022-08-alma-witn ... f-war.html

Image
by Amy C. Oliver, National Radio Astronomy Observatory
While observing a newly-dormant galaxy using the Atacama Large Millimeter/submillimeter Array (ALMA) and the Hubble Space Telescope (HST), scientists discovered that it had stopped forming stars not because it had used up all of its gas but because most of its star-forming fuel had been thrown out of the system as it merged with another galaxy. The result is a first for ALMA scientists. What's more, if proven common, the results could change the way scientists think about galaxy mergers and deaths. The results of the research are published in The Astrophysical Journal Letters.

As galaxies move through the universe, they sometimes encounter other galaxies. As they interact, each galaxy's gravity pulls on the other. The ensuing tug-of-war flings gas and stars away from the galaxies, leaving behind streams of material known as tidal tails.

And that's just what scientists believe happened to SDSS J1448+1010, but with a plot twist. The massive galaxy, which was born when the universe was about half its current age, has nearly completed merging with another galaxy. During observations with the HST and ALMA—an international collaboration in which the U.S. National Science Foundation's National Radio Astronomy Observatory (NRAO) is a partner—scientists discovered tidal tails containing roughly half of the entire system's cold, star-forming gas. The discovery of the forcefully discarded material—equal to 10 billion times the mass of Earth's sun—was an indication that the merger may be responsible for snuffing out star formation, and that's something scientists didn't expect.
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Re: Stars, supernovae, black holes and stellar remnants

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Ten new pulsating variable stars discovered
https://phys.org/news/2022-08-ten-pulsa ... stars.html
by Tomasz Nowakowski , Phys.org
By analyzing the data from NASA's Transiting Exoplanet Survey Satellite (TESS), Turkish astronomers have detected 10 new pulsating variable stars, including five Delta Scuti variables. The finding is reported in a paper published August 25 on the arXiv pre-print server.

Detecting and studying variable stars could offer important hints into aspects of stellar structure and evolution. Investigation of variables could be also helpful for a better understanding of the distance scale of the universe. In general, there are two main-sequence A-F type pulsating variables: Delta Scuti and Gamma Doradus stars.

Delta Scuti stars are pulsating variables with spectral types between A0 and F5, named after the Delta Scuti variable in the constellation Scutum. They exhibit radial and non-radial pulsations spanning periods from 20 minutes to eight hours. Studying pulsation behavior of Delta Scuti variables could help us advance our knowledge about stellar interiors. When it comes to Gamma Doradus stars, they are dwarf and/or sub-dwarf variables with a spectral type of A7-F5 and periods on the order of one day.

Now, a team of astronomers led by Filiz Kahraman Alicavus of the Çanakkale Onsekiz Mart University in Turkey, report the finding of 10 new pulsating variables by inspecting the TESS database.
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Re: Stars, supernovae, black holes and stellar remnants

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Betelgeuse’s Great Dimming: The Aftermath
by Colin Stewart
August 25, 2022

Introduction:
(Sky & Telescope) An international team of astronomers has revealed why the star Betelgeuse famously dimmed back in 2019. The dying star coughed out a huge chunk of material weighing several times more the Moon, which then blocked out some of its light.

Betelgeuse is the 10th brightest star in the night sky and marks Orion's right shoulder (his left shoulder from our point of view). It is a red supergiant, an engorged monster that would stretch out to the orbit of Jupiter if it replaced the Sun in our solar system. Betelgeuse is well on its way to ending its life by detonating as a cataclysmic supernova; meanwhile, astronomers get unprecedented insight into a giant star’s final stages.

The situation became more intriguing in late 2019 when Betelgeuse mysteriously dropped in brightness, an event that came to be known as The Great Dimming. The fading was pronounced enough, more than a magnitude, to notice even with the unaided eye. Lots of possible explanations have been mooted, but now a team led by Andrea Dupree (Center for Astrophysics, Harvard & Smithsonian) thinks they know what happened.

By piecing together data from a slew of telescopes, including the Hubble Space Telescope, Dupree is pointing the finger at an event called a Surface Mass Ejection (SME). Our own Sun regularly burps material from its corona, ejecting a billion tonnes of solar material — about the mass of Mount Everest. But Betelgeuse’s SME spit out 400 billion times more material, equivalent to several times more mass than the Moon. As the ejected material cooled, it formed a cloud of dust that partially blocked, and thus dimmed, our view of Betelgeuse.

"We've never before seen a huge mass ejection of the surface of a star,” Dupree says. “We are left with something going on that we don't completely understand.”
Read more here: https://skyandtelescope.org/astronomy- ... ftermath/

Image
A coronal mass ejection, which is distinct from a surface mass ejection, in the act.
NASA
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Re: Stars, supernovae, black holes and stellar remnants

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Red giant Betelgeuse was yellow some 2,000 years ago
https://phys.org/news/2022-09-red-giant ... years.html
by Sebastian Hollstein, Friedrich-Schiller-Universität Jena
An interdisciplinary team centered around a Jena astrophysicist utilized observations from antiquity to prove that Betelgeuse—the bright red giant star in the upper left of the constellation Orion—was yellow-orange some 2,000 years ago.

As nuclear fusion in the center of a star progresses, brightness, size, and color also change. Astrophysicists can derive from such properties important information on the age and mass of a star. Those stars with significantly more mass than our sun are blue-white or red—the transition from red to yellow and orange is relatively rapid for astronomical time-scales.

Astrophysicists of Friedrich Schiller University Jena, Germany, together with colleagues of other subjects from the U.S. and Italy, have now successfully detected and dated such a color change in a bright star. With several historical sources, they found that Betelgeuse—the bright red giant star in the upper left of the constellation Orion—was yellow-orange some 2,000 years ago. They report about their results in the current issue of Monthly Notices of the Royal Astronomical Society.
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