The death of a star is one of the most dramatic natural events in the universe. Some stars die in a supernova explosion, leaving behind nebulae as shimmering remnants of their former splendor. Some simply wither as they run out of hydrogen, turning into a red giant as they do so.
But giant black holes devour each other, and as they are destroyed, the black hole’s powerful gravity rips the star apart and funnels its gas into a donut-shaped ring around the black hole.
This is what happened about 300 million light-years away in the galaxy ESO 583-G004 when a star came very close to the galaxy’s supermassive black hole (SMBH). The interaction between the SMBH and the star is called a tidal perturbation event (TDE), and was detected by the Instrumental All-Sky Survey of Supernovae (ASAS-SN) on March 1, 2022.
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Astronomers directed the Hubble Space Telescope to observe TDE, but it struggled to watch the event unfold from such a great distance and was unable to take any pictures. However, a team of astronomers did not give up. They examined ultraviolet light from the destroyed star and extracted details of the event. They presented their findings at the 241st meeting of the American Astronomical Society.
Dubbed AT2022dsb, the TDE is one of about a hundred TDEs that astronomers have detected. Astronomers believe that in a galaxy the size of the Milky Way, a TDE occurs about once every 10,000 to 100,000 years. They are important events because there are huge gaps in our understanding of black holes and their extreme environments. Watching a star get destroyed by a black hole is one of our only glimpses at this mystifying thing.
In this case, Hubble’s powerful ultraviolet-observing capabilities came to light. Ultraviolet observations of TDE are rare, and highly desirable according to one of the astronomers involved in this research. “However, there are still very few tidal events observed in UV given the time of observation. This is really unfortunate because there is so much information you can get from UV spectra,” says Emily Engelthaler. , trained at the Center for Astrophysics | Harvard and Smithsonian (CfA) in Cambridge, Massachusetts. We’re excited that we can get these details of what the wreckage is doing. A tidal event can tell us a lot about a black hole.”
This TDE was close and bright enough to allow measurement of the event’s ultraviolet spectrum, which is unusual for events that are normally difficult to observe. Astronomers have been able to collect spectral data for a longer than usual period of time. The spectrometer revealed the presence of hydrogen, carbon, and more in the gas from the former star.
Usually, these events are difficult to monitor. You might get some notes at the beginning of the disturbance when it’s really bright. Our program is different in that it is designed to look at a few tidal events over the course of a year to see what happens,” says CfA’s Peter Maxim. “We saw this early enough that we could observe it in very intense black hole accretion stages. We’ve seen the accretion rate decrease as it has turned lower over time.”
There are some explanations involved in understanding what light from TDE means. The researchers think they are looking at a round or circular shaped gas ring that was the star. The ring is about the same size as our solar system and it orbits a black hole at the center.
“We’re looking somewhere on the edge of that donut. We’re seeing stellar winds from the black hole sweep across the surface being projected toward us at 20 million miles per hour (three percent the speed of light), says Maxime.” We’re really still making our heads spin. about this event. It rips the star apart and then it gets this material that makes its way into the black hole. And so you have models where you think you know what’s going on, and then you actually have what you see. This is an exciting place for scientists to be: right at the interface of the known and the unknown.”
In the popular imagination, black holes are voracious devourers of stars and other matter. Nothing, not even light, could escape their grasp. The most powerful black holes are the giant ones that lie at the center of galaxies like our own: supermassive black holes (SMBH,) and, as this work shows, can devour entire stars.
It’s all true, but small and medium-sized businesses do more than just consume the stuff. They also glow brightly in X-ray, ultraviolet, and optical light, and can occasionally emit energetic jets back into their galaxy as part of a poorly understood process called black hole feedback. This is part of how SMBHs and galaxies are closely related. In a way, its growth and development are interconnected, but there are many unanswered questions.
This is what makes TDEs so important. One of the only opportunities for astrophysicists to study the SMBH is when the star gets too close. The energy released from the event provides a window into the physics of black holes.
TDEs were mostly theoretical until the last few years. Now they are the subject of intense observations. TDEs allow astrophysicists to watch small and medium-sized binaries produce winds and turn jets on and off as they consume a star. And in the near future we should find more of them.
The names of tidal events usually start with the letters AT which stands for Astrophysical Transient. Transients are things that change rapidly in one way or another over time. They either flash or ignite, or move through space in short periods of time. Some TDEs, like the ones in this research, have been found by surveys of supernovae, and supernovae are just one of the transient types.
Our ability to detect transients will take a huge leap starting in 2023 when the Vera Rubin Observatory will see first light. It will scan the entire available sky each week and detect large numbers of transients, including TDEs. Upcoming telescopes such as the Large Magellan Telescope and the European Very Large Telescope will be alerted to these events and can monitor them quickly.
We have a lot of unanswered questions about supermassive black holes. We want to know more about how their growth and evolution relate to the galaxy they host. We want to know more about black hole observations. We want to know everything we can about these weird things as the physics break down.
We may only find answers by observing one TDE at a time.