A strange transient was discovered, ejecting 10% of the mass of the sun at a speed exceeding 55% of the speed of light

Astronomers have discovered a new astronomical transient in the universe that is faster, heavier and brighter at radio wavelengths than its mysterious predecessor. Astronomers have observed a bright burst in a small galaxy 500 million light-years from Earth, and a team led by Northwestern University determined that it is the third fast blue optical transient (FBOT) ever captured in radio and X-ray wavelengths. As a family of high-luminosity cosmic explosions, blue optical transients have a record of surprising astronomers with their rapid, energetic and powerful bursts of energy.

As their name implies, transients fade almost as quickly as they appear, and perhaps the most famous blue optical transient is AT2018COW, a rare event that appears to be the birth of a black hole or neutron star. But the newly discovered blue optical transient, named CRTS-CSS161010J045834-081803 or CSS161010 for short, pales in comparison to the sheer speed and extent of mass loss from its outflow. In fact, CSS161010 produces some of the fastest outflows in nature, launching gas and particles at more than 55% the speed of light.

Its incredibly fast outflow of material is also the most massive of its kind ever recorded. "This is unexpected," said Deanne Coppejans of Northwestern University, the study's first author. "We know there are high-energy explosions that can eject material at almost the speed of light, especially gamma-ray bursts, but they only eject small amounts of mass, about one millionth the mass of the sun. CSS161010 ejected 1 to 10 percent of the sun's mass at more than half the speed of light, so this evidence suggests this is a new transient." Raffaella Margutti of Northwestern University, the senior author of the study, said:

"We know what causes the fastest outflows in nature, and there are only two ways to produce them: a gamma-ray burst collapsing a massive star, or two neutron stars merging. With this study, we've introduced a third way that these outflows could be launched. There's a new beast out there that's capable of producing the same energetic phenomenon," said Margutti, an assistant professor of physics and astronomy in Northwestern's Weinberg College of Arts and Sciences and a member of Ciera, the Center for Interdisciplinary Exploration and Research in Astrophysics.

Strange supernova explosion

A blue optical transient (FBOT) is a cosmic explosion first detected at optical wavelengths. Hot enough to glow blue, a blue optical transient reaches peak brightness within a few days and then quickly decays, much faster than a standard supernova rises and decays. Although blue optical transients were recognized as early as 2014, astronomers thought these strange anomalies had been present in the night sky for much longer. These may have been in the astronomical record archives for a long time, but no one realized they were any different.

Astronomers have seen unexplained phenomena in other galaxies, but without access to information beyond optical wavelengths, researchers were unable to study them further and could only call them 'exotic supernova explosions.' The research team combined multiple observatories to gather more insight into these mysterious explosions. In 2016, researchers with the Catalina Real-Time Transient Survey and All-Sky Automated Supernova Survey (ASAS-SN) independently discovered CSS161010 at optical wavelengths. Then, a team from ASAS-SN reached out to the research team for this study to take a closer look, using their expertise in X-rays and radio waves.

Because Northwestern has remote access to the Keck Observatory, which houses the largest optical and infrared telescopes in the United States, it was able to observe the event directly. Optical wavelengths can tell us that the particles in the explosion were moving more slowly, but 'slowly moving' still about 10,000 kilometers per second. If you want to see faster particles, you have to use X-rays and radio waves, which can then be put together to see a more complete picture. Although the astrophysicists concluded that CSS161010 was definitely a blue optical transient, its true, underlying nature may never be known.

It simply burned up and then disappeared quickly, but astronomers still have a guess. Research believes that this is a very rare stellar explosion. Although the possibility is small, CSS161010 may be a star that was swallowed by a medium-sized black hole. AT2018COW and CSS161010 are very different in the speed at which they can accelerate these outflows of matter, but they do have one thing in common: the presence of a black hole or neutron star inside, and this is the key factor.

Bo Ke Yuan | Research/From: Northwestern University

The research was published in the journal Astrophysics

Research paper DOI: 10.3847/2041-8213/ab8cc7

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