Many objects including our Earth and Sun will never become black holes. Their gravity is not sufficient to overpower the atomic and nuclear forces of their interiors, which resist compression.
But in more massive objects, gravity ultimately wins. Stellar-mass black holes are born with a bang. A team of astronomers using Hawaii's ATLAS telescopes saw it on June 16, , and flagged the object to other astronomers on June 17 —triggering a rush of telescopes turning to point at the explosion.
The Cow isn't the first flash of its kind spotted in the night sky, but it is the closest one ever detected, giving researchers an unprecedented chance to see one in detail. It also got really bright, really fast.
At the Cow's peak, it was tens of times more luminous in x-rays than normal stellar explosions, which are called supernovae. The Cow hit its peak brightness in just a few days, while it takes regular supernovae weeks to fully ramp up. What's more, the Cow's power source wasn't immediately obvious. Normally, supernovae get their explosive oomph from nickel, a radioactive isotope stuffed in their innards.
But when astronomers calculated how much debris the Cow had thrown off, they came up with a surprisingly low amount of total ejected debris—maybe a tenth of our sun's mass, if that. That's weird, because supernovae normally eject tens of suns' worth of debris. This image shows a small portion of the Cygnus Loop supernova remnant.
The formation shown here marks the outer edge of an expanding blast wave from a colossal stellar explosion that occurred about 15, years ago. The blast wave slams into clouds of interstellar gas, causing it to glow and revealing information about the composition of the gas. Even if the Cow's debris were entirely nickel, that wouldn't be enough fuel to power the observed explosion. What's more, the debris contained hydrogen and helium, which astronomers weren't expecting to find: The stars that explode into supernovae should have long since burned through those elements as nuclear fuel.
The Cow also gave off radiation in unusual ways. The data showed that a little over a week after it first appeared, the Cow unexpectedly grew a lot brighter in high-energy x-rays. This object, whatever it is, is shrouded in a distinctly asymmetrical blob of material thrown off in some kind of explosion. In the model made by Margutti's team, the debris flying from the object's poles moves faster—and gets transparent sooner—than the clouds around the object's equator.
These equatorial clouds absorbed the engine's high-energy x-rays, which made the clouds heat up and generate the Cow's visible light. But some of the high-energy x-rays could still leak out from the Cow's clearer poles. Meanwhile, the Cow's radio signals show that it behaved like a bull in a foggy china shop. A paper about the findings appears in the journal Science on September 3. Hallinan and his team look for so-called radio transients—short-lived sources of radio waves that flare brightly and burn out quickly like a match lit in a dark room.
Radio transients are an excellent way to identify unusual astronomical events, such as massive stars that explode and blast out energetic jets or the mergers of neutron stars. This source is tied for the brightest radio transient ever associated with a supernova. Dong determined that the bright radio energy was originally a star surrounded by a thick and dense shell of gas.
This gas shell had been cast off the star a few hundred years before the present day. Yet, the gas shell itself, and the timescale on which it was cast off from the star, were unusual, so Dong suspected that there might be more to the story of this explosion. Following Dong's discovery, Caltech graduate student Anna Ho PhD '20 suggested that this radio transient be compared with a different catalog of brief bright events in the X-ray spectrum.
Some of these X-ray events were so short-lived that they were only present in the sky for a few seconds of Earth time. Through careful analysis, Dong established that the X-rays and the radio waves were likely coming from the same event. These two events have never been associated with each other, and on their own they're very rare. Explore further. More from Astronomy and Astrophysics. Use this form if you have come across a typo, inaccuracy or would like to send an edit request for the content on this page.
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Credit: R. More information: Mao, Junjie, et al. The Astrophysical Journal Letters arXiv HE] arxiv. Source Universe Today.
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