This artist's concept depicts a
supermassive black hole in the process of shredding a massive star—at least 30
times the mass of our sun—to pieces. Scientists propose this is what happened
around the distant black hole referred to as J2245+3743. Credit: Caltech/R.
Hurt (IPAC)
The
most massive stars in the universe are destined to explode as brilliant
supernova before collapsing into black holes. Yet one huge star appears to have
never fulfilled its destiny; in a twist of irony, the star wandered too close
to a gargantuan black hole, which gobbled it up, shredding the star to bits and
pieces.
That is the most likely explanation to
come from authors of a new study published in Nature
Astronomy describing the most powerful and most distant flare of
energy ever recorded from a supermassive black hole.
The cosmic object was first observed in
2018 by the Zwicky Transient Facility (ZTF), based at Caltech's Palomar
Observatory, and the Caltech-led Catalina Real-Time Transient Survey. The flare
rapidly brightened by a factor of 40 over a period of months, and, at its peak,
was 30 times more luminous than any previous black hole flare seen to date. At its
brightest, the flare shined with the light of 10 trillion suns.
The
supermassive black hole behind the flare is a type of accreting, or feeding,
black hole called an active galactic nucleus (AGN). Referred to as J2245+3743,
this AGN is estimated to be 500 million times more massive than our sun. It
resides 10 billion light-years away in the remote universe. Because light has a
finite speed and takes time to reach us, astronomers observe distant events
like this one in the past, when the universe was young.
"The
energetics show this object is very far away and very bright," says study
lead author Matthew Graham, research professor of astronomy at Caltech, as well
as the project scientist for ZTF, and a co-principal investigator of the
project. "This is unlike any AGN we've ever seen."
Astronomers
are continuing to monitor the black hole flare though it is fading over time.
In fact, in addition to witnessing the object in the past, time itself runs
slower at the remote site of the black hole compared to our own experience of
time.
"It's
a phenomenon called cosmological time dilation due to stretching of space and
time. As the light travels across expanding space to reach us, its wavelength
stretches as does time itself," Graham explains, noting that long-lived
surveys like ZTF and Catalina are important to fully witness events in the past
because, in this case, "seven years here is two years there. We are
watching the event play back at quarter speed."
To
determine what could cause such a dramatic burst of light in the cosmos, the
researchers thoroughly examined a list of possibilities, concluding that the
most likely culprit is a tidal disruption event (TDE). This phenomenon occurs
when a supermassive black hole's gravity shears a star that comes too close,
slowly consuming the star over time as it spirals into the black hole. The fact
that the black hole flare J2245+3743 is still going indicates that we are
witnessing a star not yet fully devoured but rather like "a fish only
halfway down the whale's gullet," Graham says.
If the flare is from a TDE, the scientists estimate that the supermassive black hole gobbled a star with a mass at least 30 times greater than that of our sun. The previous record holder for the largest candidate TDE, an event nicknamed Scary Barbie after its initial ZTF classification as ZTF20abrbeie, was not nearly as intense. That TDE, which is also thought to have originated from an AGN, was 30 times weaker than that of J2245+3743, and its doomed star is estimated to have been between three and 10 solar masses.
Stellar snack within a black hole's disk
Most of the roughly 100 TDEs seen
to date do not take place around AGN—massive structures that consist of
supermassive black holes surrounded by large, swirling disks of material
that feed the central black hole. The AGN burble along, flaring up with their
own feeding activity, which can mask TDE bursts and makes them harder to find.
The recent jumbo flare J2245+3743, on the other hand, was so large that it was
easier to see.
However, at first, J2245+3743 did
not seem to be anything special. In 2018, after the object was first spotted,
the researchers used the 200-inch Hale Telescope at Caltech's Palomar
Observatory to obtain a spectrum of the object's light, but it did not reveal
anything unusual. In 2023, the team noticed the flare was decaying slower than
expected, so they obtained another spectrum from the W. M. Keck Observatory in
Hawai'i, which indicated the extreme brightness of this particular AGN.
"At first, it was important to
establish that this extreme object was truly this bright," explains
co-author K. E. Saavik Ford, a professor at the City University of New York
(CUNY) Graduate Center and Borough of Manhattan Community College and American
Museum of Natural History (AMNH).
It was possible, she says, that the
object could have been beaming the light toward us rather than glowing in all
directions, but data from NASA's former Wide-field Infrared Survey Explorer
(WISE) mission helped rule that out. In the end, after other scenarios were
also ruled out, the researchers concluded that J2245+3743 was indeed the
brightest black hole flare ever recorded.
"If you convert our entire sun
to energy using Albert Einstein's famous formula E = mc2, that's how much energy has been pouring out from this flare since we
began observing it," Ford says.
Once the team established the
unprecedented brightness of the event, they looked at what could possibly have
caused it. "Supernovae are not bright enough to account for this,"
Ford says, referring to one possibility. Instead, the team's favored
explanation is a supermassive black hole slowly ripping a huge star to death.
"Stars this massive are
rare," Ford says, "but we think stars within the disk of an AGN can
grow larger. The matter from the disk is dumped onto stars, causing them to
grow in mass."
Finding a black hole meal with such
mega proportions indicates that other events like this are likely taking place
across the cosmos. The researchers hope to mine through more ZTF data to find
others, and the NSF and Department of Energy's Vera C. Rubin Observatory may
likewise find unusually large TDEs.
"We never would have found
this rare event in the first place if it weren't for ZTF," Graham says.
"We've been observing the sky with ZTF for seven years now, so when we see
anything flare or change, we can see what it has done in the past and how it
will evolve."
Source: Unprecedented black hole flare spotted 10 billion light-years away
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