Stars, supernovae, black holes and stellar remnants

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World's first 3D simulations reveal the physics of exotic supernovae
https://phys.org/news/2023-09-world-3d- ... ysics.html
by ASIAA

After years of dedicated research and over 5 million supercomputer computing hours, a team has created the world's first high-resolution 3D radiation hydrodynamics simulations for exotic supernovae. This work is reported in The Astrophysical Journal.

Ke-Jung Chen at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan, led an international team and used the powerful supercomputers from the Lawrence Berkeley National Laboratory and the National Astronomical Observatory of Japan to make the breakthrough.

Supernova explosions are the most spectacular endings for massive stars, as they conclude their life cycles in a self-destructive manner, instantaneously releasing brightness equivalent to billions of suns, illuminating the entire universe.

During this explosion, heavy elements formed within the star are also ejected, laying the foundation for the birth of new stars and planets and playing a crucial role in the origin of life.

Supernovae are a key interest in modern astrophysics, encompassing numerous important astronomical and physical issues in both theory and observation, holding significant research value.

Over the past half-century, research has provided a relatively comprehensive understanding of supernovae. However, the latest large-scale supernova survey observations are revealing many unusual stellar explosions (exotic supernovae) that challenge and overturn previously established understanding of supernova physics.

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Supermassive Black Holes Alter Galactic chemistry
September 15, 2023

Introduction:

(Eurekalert) New research shows that the supermassive black hole at the center of a galaxy can have a direct impact on the chemical distribution of the host galaxy. This provides another piece of the puzzle for understanding how galaxies evolve.

It is well known that active supermassive black holes can produce major changes their host galaxies by heating up and removing the interstellar gas in the galaxy. But the compact sizes of black holes, the long distances from Earth, and obscuration by dust in the galaxies have made it difficult to measure the chemical composition distribution of the gas around an active supermassive black hole.

In this study, an international team of researchers led by Toshiki Saito at the National Astronomical Observatory of Japan and Taku Nakajima at Nagoya University used ALMA (Atacama Large Millimeter/submillimeter Array) to observe the central region of Messier 77 located 51.4 million light-years away in the direction of the constellation Cetus. Messier 77 is a relatively nearby example of a galaxy hosting an active supermassive black hole.

Thanks to ALMA’s high spatial resolution and a new machine learning analysis technique, the team was able to map the distribution of 23 molecules. This is the first survey to objectively depict the distribution of all detected molecules through unbiased observations. The results show that along the path of the bipolar jets emanating near the black hole, molecules commonly found in galaxies such as carbon monoxide (CO) seem to break down, while the concentrations of distinctive molecules such as an isomer of HCN and the cyanide radical (CN) increase. This is direct evidence that supermassive black holes affect not only the large-scale structure, but also the chemical composition of their host galaxies.

Read more of the Eurekalert article here: https://www.eurekalert.org/news-releases/1001703

For a technical presentation of the results of the study as presented in The Astrophysical Journal: https://iopscience.iop.org/article/10. ... 57/ace4c7

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[wjfox]

First evidence of spinning black hole detected by scientists

Wed 27 Sep 2023 18.31 BST

Astronomers have captured the first direct evidence of a black hole spinning, providing new insights into the universe’s most enigmatic objects.

The observations focus on the supermassive black hole at the centre of the neighbouring Messier 87 galaxy, whose shadow was imaged by the Event Horizon Telescope. Like many supermassive black holes, M87 features powerful jets that are launched from the poles at close to the speed of light into intergalactic space.

Scientists have predicted that the rotation of a black hole powers these cosmic jets, but until now direct evidence was elusive.

“After the success of black hole imaging in this galaxy with the Event Horizon Telescope, whether this black hole is spinning or not has been a central concern among scientists,” said Dr Kazuhiro Hada, of the national astronomical observatory of Japan and co-author. “Now anticipation has turned into certainty. This monster black hole is indeed spinning.”

M87 is located 55m light years from the Earth and harbours a black hole 6.5bn times more massive than the Sun. Just beyond the black hole is an accretion disk of gas and dust, swirling on the precipice of the cosmic sinkhole. Some of this material is destined to fall into the black hole, disappearing for ever. But a fraction will be ejected out from the poles of the black hole at more than 99.99% of the speed of light.

https://www.theguardian.com/science/202 ... scientists

[wjfox]

Living on the edge: Supernova bubble expands in new Hubble time-lapse movie

September 28, 2023

Though a doomed star exploded some 20,000 years ago, its tattered remnants continue racing into space at breakneck speeds—and NASA's Hubble Space Telescope has caught the action.

The nebula, called the Cygnus Loop, forms a bubble-like shape that is about 120 light-years in diameter. The distance to its center is approximately 2,600 light-years. The entire nebula has a width of six full moons as seen on the sky.

Astronomers used Hubble to zoom into a very small slice of the leading edge of this expanding supernova bubble, where the supernova blast wave plows into surrounding material in space. Hubble images taken from 2001 to 2020 clearly demonstrate how the remnant's shock front has expanded over time, and they used the crisp images to clock its speed.

By analyzing the shock's location, astronomers found that the shock hasn't slowed down at all in the last 20 years, and is speeding into interstellar space at over half a million miles per hour—fast enough to travel from Earth to the moon in less than half an hour. While this seems incredibly fast, it's actually on the slow end for the speed of a supernova shock wave. Researchers were able to assemble a "movie" from Hubble images for a close-up look at how the tattered star is slamming into interstellar space.

"Hubble is the only way that we can actually watch what's happening at the edge of the bubble with such clarity," said Ravi Sankrit, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland. "The Hubble images are spectacular when you look at them in detail. They're telling us about the density differences encountered by the supernova shocks as they propagate through space, and the turbulence in the regions behind these shocks."

[see link below for movie]

https://phys.org/news/2023-09-edge-supe ... movie.html



Credit: NASA, ESA, Ravi Sankrit (STScI)

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Strange Rare Star Explosion Spied by Hubble Where It Shouldn't Be
by Dr. Alfredo Carpineti
October 6, 2023

Introduction:

(IFL Science) For the last five years, astronomers have been spotting peculiar stellar explosions that don’t behave like any other known. These rare events are known as Luminous Fast Blue Optical Transients (LFBOT) – you may even remember the first one, nicknamed the "Cow" (AT2018cow). Already strange, they just got stranger as Hubble has observed one happening where it definitely shouldn't be.

LFBOTS are among the brightest visible events in the universe but they are very rare; on average, just one a year has been discovered since 2018. They are similar to supernovae or gamma-ray bursts, becoming incredibly bright but they fade away in a matter of days, unlike supernovae that take weeks or months.

The best explanation for them has been considered a special type of supernova from extremely massive stars. These LFBOTs happen in the spiral arms of star-forming galaxies, which is exactly where massive stars would live their extremely short lives. So imagine astronomers' surprise when they tracked one of these events with Hubble and found it happening in intergalactic space.

AT2023fhn, nicknamed the "Finch”, has all the characteristics of the other handful of LFBOT discovered so far apart from its location inexplicably in the empty space between two galaxies. It's about 50,000 light-years from the large spiral galaxy and about 15,000 light-years from the small galaxy.
"The more we learn about LFBOTs, the more they surprise us," said lead author Ashley Chrimes, a European Space Agency Research Fellow, in a statement. "We've now shown that LFBOTs can occur a long way from the center of the nearest galaxy, and the location of the Finch is not what we expect for any kind of supernova."

Read more here: https://www.iflscience.com/strange-rar ... e-71007

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Supermassive Black Holes Posses A Strange Mechanism That Prevents Overeating
by Kiona Smith
November 2, 2023

Introduction:

(Inverse) We think of supermassive black holes as gorging cosmic monsters, swallowing up anything that gets too close, but according to a recent study, the supermassive black hole at the heart of a nearby galaxy called Circinus is actually a very picky eater.

Astrophysicist Takuma Izumi, of the National Astrophysical Observatory of Japan, and his colleagues used ALMA to take the highest-resolution look yet at the center of Circinus, and they found that the black hole only consumes about 3 percent of the gas that falls toward it. Radiation — released by material racing faster and faster as it spirals toward the supermassive black hole — pushes the rest of the gas back into the galaxy in fast-moving, turbulent streams. The researchers published their work in the journal Science.

Izumi and his colleagues used the Atacama Large Millimeter/submillimeter Array — 66 radio telescope antennas in the highlands of Chile — to map the flow of gas in the innermost region of the Circinus galaxy, 13.05 million light years away.

Specifically, they watched the innermost 1 percent of the galaxy, spanning a distance from about 325 light years to about 32.5 light years from the supermassive black hole., which is about 1.7 million times more massive than our Sun. That’s such a narrow area that it’s hard to see in much detail, but ALMA’s array of radio dishes let Izumi and his colleagues watch the action with about 1.6 to 8.5 light-year resolution. And what they saw was the black hole shoving away most of the gas that fell toward it.

The ALMA data revealed a messy, chaotic disk of gas swirling around the black hole. As gas falls inward from farther out in the galaxy, it ends up in what’s called an accretion disk: a spiral of material swirling around the black hole, accelerated to tremendous speeds by the black hole’s powerful gravity.

Read more here: https://www.inverse.com/science/superm ... -galaxy