Starship Asterisk*

Colin Stuart of Sky & Telescope wrote:

Some massive stars may collapse completely into black holes — without the fanfare of a supernova.

An international team of astronomers has revealed a black hole that seems to have formed without the usual supernova explosion. By probing exactly how this happened, they've helped cement a long-held suspicion that this mechanism is responsible for a host of disappearing stars.

When a massive star reaches the end of its life, it usually erupts in a cataclysmic celestial fireworks display...

But do massive stars always detonate like this? Not according to a team of astronomers led by Alejandro Vigna-Gómez (Max Planck Institute for Astrophysics, Germany). Their work centers on a binary system in the Large Magellanic Cloud known as VFTS 243...

When a star dies in a supernova, the material is usually ejected asymmetrically, leading to a kick that sends the stellar remnant surging off across space... Yet the two objects in the VFTS 243 system remain in an almost perfectly circular orbit around one another. If the black hole experienced a kick when it formed, then it must have been only a small one...

In fact, the team concludes that the original star lost only a small amount of mass — up to a third of a Sun — when its dense core collapsed. Rather than casting off its outer layers in a supernova, the collapse released energy primarily through a symmetrical ejection of neutrinos. The resulting kick to the newly formed black hole was just 4 kilometers per second...

Although not an open-and-shut case just yet, the direct collapse of black holes could help solve an enduring astronomical mystery. Previous efforts such as the Vanishing and Appearing Sources during a Century of Observations (VASCO) project have identified 100 stars that suddenly disappeared from the night sky over the last 70 years. If these stars collapsed directly into black holes, without supernova fanfare, that could explain their sudden vanishing act.

Christian G. wrote: ↑Tue May 28, 2024 2:32 pm Thanks for this most interesting link! I wonder if another consideration that might support the idea of stars vanishing into back holes is that of supernovae (type II) as rebounds - what's there to rebound against when a star collapses into a black hole?
(might the two even be related - no rebound, therefore no kick?)

Ann wrote: ↑Tue May 28, 2024 4:56 pm

Christian G. wrote: ↑Tue May 28, 2024 2:32 pm Thanks for this most interesting link! I wonder if another consideration that might support the idea of stars vanishing into back holes is that of supernovae (type II) as rebounds - what's there to rebound against when a star collapses into a black hole?
(might the two even be related - no rebound, therefore no kick?)

I have also heard of the word rebound when it comes to most supernovas. I searched for a video showing this rebound, but was unsuccessful. The best video I found was this one, "How does a supernova explode", where, unfortunately, the narrator speaks French. Even though there are subtitles, I found it hard to concentrate.

Nevertheless, this much is clear from the video: The supernova happens because of the way that the infalling matter interacts with the newly formed neutron star at the stellar core. The way I understand it, the newly formed neutron star is essential for the making of the supernova, so, therefore, if there is no neutron star, we don't get a supernova. At least not a brilliant supernova that blows a huge amount of matter out into space.

If there is no neutron star, but the black hole forms directly, perhaps there simply is no supernova? The star merely "winks out"?

This pair of visible-light and near-infrared photos from NASA's Hubble Space Telescope shows the giant star N6946-BH1 before and after it vanished out of sight by imploding to form a black hole. The left image shows the star, which is 25 times the mass of our sun, as it looked in 2007. In 2009, the star shot up in brightness to become over 1 million times more luminous than our sun for several months. But then it seemed to vanish, as seen in the right panel image from 2015. A small amount of infrared light has been detected from where the star used to be. This radiation probably comes from debris falling onto a black hole. The black hole is located 22 million light-years away in the spiral galaxy NGC 6946. Credit: NASA/ESA/C. Kochanek (OSU)

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Read more here.

Ann