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Astrophysicists capture new class of astronomical transient objects

The newly identified FBOT which is called CRTS-CSS161010 J045834-081803 or CSS161010 in short has vastly overshadowed the previously discovered FBOT “The Cow” with the heaviness and sheer speed of its material outflows.

May 27, 2020 18:11 IST
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A new astronomical transient that is faster, brighter, and heavier at radio wavelengths than its mysterious predecessors has been captured in the universe by the astrophysicists.

After a bright burst was visually captured, in 2016, by the astronomers in a tiny galaxy 500 million lightyears away from Earth, a Northwestern University-led team determined that the anomaly is the third fast blue optical transient (FBOT) ever captured in X-ray and radio wavelengths.

FBOTs, a highly luminous family of cosmic explosions, have a track record of surprising astronomers with their energetic, fast, and powerful bursts of energy. The most famous FBOT is AT2018COW (“The Cow”)- a rare event that appeared to be the birth of a neutron star or black hole. But the newly identified FBOT has vastly overshadowed the cow.

New FBOT in the Universe:

The newly identified FBOT which is called CRTS-CSS161010 J045834-081803 or CSS161010 in short has vastly overshadowed the previously discovered FBOT “The Cow” with the heaviness and sheer speed of its material outflows.

It has, in fact, produced some kind of fastest outflows in nature launching particles and gas at more than 55% the speed of the light. Its fastest outflows have been documented as the heaviest for its class.

Northwester’s Deanne Coppejans, the first author of the study states that this was unexpected. Energetic explosions are known that can eject the material at almost the speed of the light, especially gamma-ray bursts, but they launch only a small amount of mass- that is 1 millionth of the sun. CSS161010 has launched 1 to 10 percent the mass of the sun at more than half the speed of light which shows that this is a new class of transient.

Raffaella Margutti from Northwestern who is a senior author of the study mentions that though we were aware of what produced the fastest outflows in nature and it was assumed by the researchers that there were only two ways of producing them- two neutron stars merging or by collapsing a massive star with a gamma-ray burst. But with this study, a third way has been introduced to launch these outflows. As per Margutti, there is a new beast out there and is able to produce the same energetic phenomenon. The Research was published on May 26, 2020 in The Astrophysical Journal Letters.

FBOT: Weird supernovae

FBOT is basically a type of cosmic explosion that was initially detected in the optical wavelength. As their name applies, transient fades almost as quickly as they appear. They are so hot that they glow blue. They reach their peak brightness within a matter of days and then quickly fade which is much faster than the standard supernovae’s rise and decay.

Although, FBOTs were recognized by the astronomers as their own class in 2014, but it has been assumed that these curious anomalies have been dotting our night sky for a much longer time.

As per Margutti, they probably have been inside our archives for a long time but we were not able to recognize them as anything different. However, the glitches in other galaxies were observed that couldn’t be explained but researchers were unable to get the information outside the optical wavelength, so they could not have been examined further. They were just called ‘weird supernovae’.

Study of new FBOT ‘CSS161010’

Margutti’s team combined multiple observations in order to get more insights into these mysterious explosions. Researchers at The All-Sky Automated Supernova Survey (ASAS-SN) and Catalina Real-Time Transient Survey, in 2016, had independently spotted CSS161010 with optical wavelengths. ASAS-SN team had then approached Coppejans and Margutti to take a closer look at using their expertise in radio waves and X-rays.

They were able to observe the phenomenon directly as Northwestern has remote access to the Keck Observatory that has the largest Optical and infrared Telescopes in the United States.

Margutti explained that the optical wavelength can inform about the particles moving slowly in an explosion but moving slowly is still 10,000 kilometres per second. To observe faster particles, X-rays and radio waves must be used. Then one can put them all together to see a more complete picture.

Even though the astrophysicists were able to conclude that CSS161010 is an FBOT, they may still never know its true, underlying nature. It flared up and faded too quickly. Still, there has been a guess.

As per Coppejans, it is a very rare type of stellar explosion, although it is less likely that CSS161010 could instead be a star that was being eaten by a medium-sized black hole.

Margutti had further mentioned that CSS161010 and The Cow were very much different in how fast they were able to speed up these outflows. But one thing that they share is- the presence of a neutron star or a black hole inside, which is a key ingredient.

Strange home of CSS161010:

Before CSS161010 was spotted by the astronomers, they had not noticed the tiny galaxy in which it has been residing. The bright FBOT drew attention to a dwarf galaxy which is near the constellation Eridanus, which has a shape of a river in the southern celestial hemisphere.

This host galaxy contains about 10 million stars while the milky way comprises billions. The Northwestern researchers were able to glimpse the tiny galaxy as they have remote access to the Keck Telescopes in Hawaii. The galaxy looked like nothing more than a small smudge.

The astronomers have so far only found FBOTs like the Cow and CSS161010 in these tiny galaxies which gives a clue in their nature. Even though Coppejans and Margutti have not yet fully explored these clues, they have been speculating the tiny galaxies might be harboring transients as these galaxies contain such low levels of metals.

A Postdoctoral Associate at CIERA, Giacomo Terraran has taken the keck observations to investigate the galaxy and help to understand the FBOT within it.

As per Terraran, every time neutron stars emerge or a star dies, they give metals back to the environment. Tiny galaxies have tiny amounts of metals as not many stars have died there. This impacts on how other stars live their lives. It has been believed that it is not by chance that these very rare transients can be found in these tiny galaxies.

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