- 4149 - BLACK HOLE - switched on? A Black Hole switched on in the blink of an eye? In 2019, astronomers discovered one of the most powerful transients ever seen, where astronomical objects change their brightness over a short period. Astronomers were searching for the source of a gravitational wave (GW) that was thought to be caused by two massive objects merging in our galaxy.
-------------- 4149 - BLACK HOLE - switched on?
- Multiple follow-up observations were made
and the combined observations and spectra revealed that the source was a
supermassive black hole (SMBH) in a distant galaxy that mysteriously “switched
on,” becoming one of the most dramatic bursts of brightness ever seen with a
black hole.
-
- The astronomers found “J221951” while
searching for the progenitor of a gravitational wave (GW) event (S190930t)
detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and
Advanced Virgo detector on April 1st, 2019.
-
- “Swift” was one of several observatories
participating in the search for the sources of GW candidates released by the
LIGO-Virgo collaboration. Based on the GW signal, the event was thought to be
the result of a kilonova, where two neutron stars merge (or a neutron star and
a black hole), releasing a tremendous amount of energy and gravitational waves
in the process.
- Kilonova events typically appear as bright
blue bursts that fade and turn redder over the next few days. With Swift they
noticed that the transient did not appear blue or change color or fade as
rapidly as expected. Follow-up observations with Hubble‘s Cosmic Origins
Spectrograph (COS) obtained ultraviolet spectra from J221951, which revealed
that it was not associated with the previously-detected GW event.
-
- The spectra further indicated that the
source was about 10 billion light-years distant, whereas the GW signal was
detected less than 0.5 billion light-years away. J221951 resulted from an SMBH that consumed
surrounding material suddenly and rapidly. This was confirmed by optical and
infrared data that previously detected a red galaxy in the vicinity of J221951,
and the location of the bright burst is consistent with the galaxy’s center.
-
- Furthermore, the UV spectra showed
absorption features consistent with a huge release of energy, which pushed and
was absorbed by gas and dust surrounding the black hole. Combined with its
brightness, the data revealed that J221951 is one of the most dramatic events
ever seen where a black hole suddenly “switched on.”
-
- This discovery is part of a growing body of
research that shows how SMBHs play a very active role in a galaxy’s star
formation. As these behemoths gobble up material, such as gas, dust, and even
stars, they release intense bursts of energy that disrupt star-forming material
within the galaxy’s central region and disk.
-
- Our understanding of the different things
that supermassive black holes can do has greatly expanded in recent years, with
discoveries of stars being torn apart and accreting black holes with hugely
variable luminosities. J221951 is one of the most extreme examples yet of a
black hole taking us by surprise.
-
- Continued monitoring of J221951 to work out
the total energy release might allow us to work out whether this is a tidal
disruption of a star by a fast-spinning black hole, or a new kind of AGN switch
on.
-
- They also identified two possible
mechanisms that could explain the sudden and voracious feeding behavior. On the
one hand, it is possible that an orbiting star passed close to the SMBH and was
pulled apart, known as a tidal disruption event (or more commonly as
“spaghettification”).
-
- A second possibility is that J221951 is an
active galactic nucleus (AGN), known as a “quasar,” that began feeding on its
accretion disk. In other words, the SMBH at the center of this galaxy “woke up”
from its previously dormant state.
-
- In the future, we will be able to obtain
important clues that help distinguish between the tidal disruption event and
active galactic nuclei scenarios. For instance, if J221951 is associated with
an AGN turning on we may expect it to stop fading and to increase again in
brightness, while if J221951 is a tidal disruption event we would expect it to
continue to fade. We will need to continue to monitor J221951 over the next few
months to years to capture its late-time behavior.
-
-
September 11,
2023 BLACK HOLE -
switched on? 4149
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Wednesday, September 13, 2023 ---------------------------------
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