Science

Polarized light reveals ultimate fate of a star “spaghettified” by a black hole

in great shape , If a star (red mark) wanders too close to the black hole (left), it may be cut, or spaghettified, by intense gravity. Some of the star’s material revolves around the black hole, such as water in a stream, emitting copious amounts of X-rays (blue).

NASA/CXC/M. weiss

When astronomers saw a star shredded, or “spaghettified,” for the first time since getting very close to a massive black hole in 2019, they determined that the optical light emitted from the explosion ejected most of the star’s matter into a powerful wind. was launched towards. , Now, astronomers at the University of California, Berkeley (UCB) have analyzed the polarization of that light to determine that the cloud was probably spherically symmetric, adding further evidence for the presence of that powerful wind.

“This is the first time anyone has estimated the size of a gas cloud around a tidal star,” said co-author Alex Filipenko, a UCB astronomer. The latest findings appeared in a recent paper published in Monthly Notices of the Royal Astronomical Society.

As we have previously reported, an object that passes beyond a black hole’s event horizon – including light – is swallowed up and cannot escape, although black holes are also mess eaters. This means that part of an object’s substance is actually ejected in a powerful jet. If that object is a star, the process of being shredded (or “spaghettified”) by the black hole’s powerful gravitational forces occurs outside the event horizon, and part of the star’s original mass is violently ejected outwards. This can form a rotating ring of matter (aka, an accretion disk) around the black hole that emits powerful X-rays and visible light. Jets are one way astronomers can indirectly predict the presence of black holes.

In 2018, astronomers captured the first direct image of a star since a black hole 20 million times more massive than our Sun in a pair of colliding galaxies called Arp 299 at a distance of about 150 million-light-years from Earth. announced. A year later, astronomers recorded the final death of a star torn apart by a supermassive black hole in such a “tidal disruption event” (TDE), called AT 2019qiz. The star had broken up with about half of its mass – or accumulated – in a black hole 1 million times the mass of the Sun, and the other half had ejected.

These powerful bursts of light are often hidden behind a veil of interstellar dust and debris, making it difficult for astronomers to study them in greater detail. But AT 2019qiz was discovered shortly after the star collapsed last year, making it easier to study in detail, before the dust and debris curtain had fully formed. Astronomers made follow-up observations across the electromagnetic spectrum over the next six months using multiple telescopes around the world. Those observations provided the first direct evidence that the gas outflow during accretion and accretion produces the powerful optical and radio emissions previously observed.

Artist's impression of a star being disrupted by the tidal wave of a supermassive black hole.
in great shape , Artist’s impression of a star being disrupted by the tidal wave of a supermassive black hole.

Astronomers knew that the optical light emitted had a modest 1 percent polarization, based on observations from the 3-meter Shane Telescope at Lick Observatory near San Jose, California; The observatory includes a spectrograph to determine the polarization of optical light. The light would have become polarized after the electrons were scattered in the gas cloud. Given how far apart such TDEs are, they are generally visible only as points of light, and polarization is one of the few properties hinting at the shape of objects.

According to co-author Kishore Patra, most of the light emerging from the accretion disk would have started in the X-ray regime, but as it passed through the gas cloud, that light continued to lose energy due to various scattering, absorption and . Revisions are finally emerging in the optical regime. “The final scattering then determines the polarization state of the photon,” Patra said. “So, by measuring the polarization, we can deduce the geometry of the surface where the final scattering occurs.”

Based on October 2019 polarization measurements showing zero polarization, Berkeley scientists calculated that the light came from a spherical cloud with a surface radius of about 100 astronomical units (au), or about 100 times larger than Earth’s orbit. Is. However, measurements taken a month later revealed a 1 percent polarization of the light, suggesting that the cloud had thinned and taken on a slight asymmetry.

“This observation rules out a class of theoretically proposed solutions and gives us a strong constraint on what happens to the gas around a black hole,” Patra said. “People are seeing other evidence of wind from these events, and I think this polarization study certainly makes that evidence stronger, in the sense that you wouldn’t get spherical geometry without a substantial amount of wind. Interesting facts here It is that a significant fraction of the material in the star that is spiraling inward does not eventually collapse into the black hole – it is blown away by the black hole.”

DOI: Monthly Notices of the Royal Astronomical Society, 2022. 10.1093/mnras/stac1727 (about DOI).

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