There is a supermassive black hole (SMBH) at the center of most galaxies. Some of them are very active, gobbling on material and ejecting powerful jets. Others live a quiet life, like Sagittarius A*, the SMBH at the center of the Milky Way.
Last month we reported on the first observation of a quiet SMBH flaring up after it ate a star, and now a team of astronomers from Johns Hopkins University were able to follow the evolution of that event in greater detail. The new research confirmed the previous study and expanded on how common tidal disruption flares are. These are expected to happen every time a star gets too close to a black hole and is ripped to shreds by its gravity.
The event, called ASASSN-14li, was followed up by different telescopes trying to characterize how tidal disruption flares are caused by black holes tearing stars apart. The stellar material is eaten by the black hole, which then emits jets. According to the study, published in Science, jets due to tidal disruption flares should be emitted by both supermassive and stellar-sized black holes, and the reason why we haven’t detected them in the black holes in our galaxy is only due to the lack of sensitivity of our instruments.
"These events are extremely rare," Sjoert van Velzen, lead author of the study, said in a statement. "It's the first time we see everything from the stellar destruction followed by the launch of a conical outflow, also called a jet, and we watched it unfold over several months."
Jets can be formed by a swirling mass of material around black holes (called accretion disks), so the researchers had to make sure that the event was actually a star being destroyed by the SMBH.
"The destruction of a star by a black hole is beautifully complicated, and far from understood," van Velzen added. "From our observations, we learn the streams of stellar debris can organize and make a jet rather quickly, which is valuable input for constructing a complete theory of these events."
Van Velzen's team at Johns Hopkins wasn't the only group searching for radio signals from ASASSN-14li – a team at Harvard University had been observing it, using radio telescopes in New Mexico. Van Velzen’s group met the other team at a workshop in Jerusalem earlier this month. It was the first time the two teams had met face-to-face, although they have been working on the same object for the last year.
"The meeting was an intense, yet very productive exchange of ideas about this source," van Velzen said. "We still get along very well; I actually went for a long hike near the Dead Sea with the leader of the competing group."
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