Black Hole is probably the most mysterious force of the universe. Recent studies have helped us to know this mysterious energy-consuming giant much better, yet we still have a long way to go.
A recent report from NASA has given us the opportunity to observe the power of this gigantic force for the first time, and it is surely mesmerizing. According to the report, NASA’s planet-hunting Transiting Exoplanet Survey Satellite (TESS) watched a black hole tear apart a star in a cataclysmic phenomenon called a tidal disruption event. Following it up, Neil Gehrels Swift Observatory and other facilities have observed the matter and produced the most detailed look yet at the early moments of one of these star-destroying moments.
We got further information from Thomas Holoien who is a Carnegie Fellow at the Carnegie Observatories in Pasadena, California. In his words,
“TESS data let us see exactly when this destructive event, named ASASSN-19bt, started to get brighter, which we’ve never been able to do before. Because we identified the tidal disruption quickly with the ground-based All-Sky Automated Survey for Supernovae (ASAS-SN), we were able to trigger multi-wave length follow-up observations in the first few days. The early data will be incredibly helpful for modeling the physics of these outbursts.”
Much information on the topic could also be found in Holoien’s paper which was published in the September 27, 2019 issue of The Astrophysical Journal.
The ASAS-SN worldwide network of 20 robotic telescopes headquartered at Ohio State University (OSU) in Columbus, reportedly discovered the star- shredding moment on January 29. Holoien received the alert from the project’s South Africa instrument while working in Chile. Thereafter he quickly arranged two Las Campanas telescopes on ASASSN-19bt. He also requested follow-up observations by Swift, European Space Agency’s XMM-Newton and ground-based 1-meter telescopes in the global Las Cumbres Observatory network.
At the same time, TESS was already observing the same area. They hunted the large sectors through the planet hunter monitors for 27 days at a time. During this observation, TESS witnessed transits, periodic dips in a star’s brightness that may indicate orbiting planets.
As the satellite started science operations on July 2018, ASAS-SN gave more attention to the TESS sectors. It was anticipated that TESS may catch the earliest light from short-lived stellar outbursts, including supernovae and tidal disruptions. And the result was positive. TESS had a first look at the ASASSN-19bt on January 21, over a week before the event was bright enough for ASAS-SN to detect it. However, the first TESS data on the tidal disruption was not available until March 13 due to some data processing policy.
The report says that it was fortunate that the disruption occurred in TESS’s southern continuous viewing zone, which was always in sight of one of the satellite’s four cameras. Therefore, ASASSN-19bt’s location allowed Holoien and his colleagues to follow the event across several sectors.
On this issue, Patrick Vallely, a co-author and National Science Foundation Graduate Research Fellow at OSU said:
“The early TESS data allow us to see light very close to the black hole, much closer than we’ve been able to see before. They also show us that ASASSN-19bt’s rise in brightness was very smooth, which helps us tell that the event was a tidal disruption and not another type of outburst, like from the center of a galaxy or a supernova”.
Holoien said that his team used the UV data from Swift — the earliest yet seen from a tidal disruption — to determine that the temperature dropped by about 50%, from around 71,500 to 35,500 degrees Fahrenheit (40,000 to 20,000 degrees Celsius), over a few days. Both Swift and XMM-Newton gave an image of a low level of X-ray emission for an unknown reason.
S. Bradley Cenko, Swift’s principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland pointed:
“People have suggested multiple theories — perhaps the light bounces through the newly created debris and loses energy, or maybe the disk forms further from the black hole than we originally thought and the light isn’t so affected by the object’s extreme gravity. More early-time observations of these events may help us answer some of these lingering questions”.
According to the astronomers, the supermassive black hole that generated ASASSN-19bt weighs around 6 million times the Sun’s mass. It also “sits at the center of a galaxy called 2MASX J07001137-6602251 located around 375 million light-years away in the constellation Volans. The destroyed star may have been similar in size to our Sun”.
As it is known to us, tidal disruptions are very rare and they occur once every 10,000 to 100,000 years in a galaxy the size of our own Milky Way, whereas Supernovae happen every 100 years or so. So far the astronomers have observed only about 40 tidal disruptions. Padi Boyd, the TESS project scientist at Goddard said:
“For TESS to observe ASASSN-19bt so early in its tenure, and in the continuous viewing zone where we could watch it for so long, is really quite extraordinary. Future collaborations with observatories around the world and in orbit will help us learn even more about the different outbursts that light up the cosmos.”
We hope that TESS will initially find more data regarding the star- shredding event and these data will help us to understand how the universe works.