Astronomers were not
entirely sure what it is. If, as they suspect, the gas ball is the result of a
supernova, then it's the most powerful supernova ever seen. In June of 2015,
astronomers viewed a ball of hot gas billions of light years away that is
radiating the energy of hundreds of billions of suns.
Even in a discipline that
regularly uses gigantic numbers to express size or distance, the case of this
small but powerful mystery object in the center of the gas ball is extreme. At
its heart is an object a little larger than 10 miles across. ASAS-SN-15lh, as
the object is known, was twice as luminous as any previously seen, far brighter
than any normal supernova, and outshone our entire Milky Way galaxy by 50
times.
The artist’s impression
below shows what it would look like from an exoplanet 10,000 light-years away
in its home galaxy.
The team reported that the object at the center could
be a very rare type of star called a magnetar--but one so powerful that it
pushes the energy limits allowed by physics. An international team of
professional and amateur astronomers spotted the possible supernova, now called
ASASSN-15lh, when it first flared to life in June 2015.
The gas ball surrounding the
object can't be seen with the naked eye, because it's 3.8 billion light years
away. But it was spotted by the All Sky Automated Survey for Supernovae
(ASAS-SN, pronounced "assassin") collaboration. Led by Ohio State,
the project uses a cadre of small telescopes around the world to detect bright
objects in our local universe.
Though ASAS-SN has
discovered some 250 supernovae since the collaboration began in 2014, the
explosion that powered ASASSN-15lh stands out for its sheer magnitude. It is
200 times more powerful than the average supernova, 570 billion times brighter
than our sun, and 20 times brighter than all the stars in our Milky Way Galaxy
combined.
"We have to ask, how is
that even possible?" said Krzysztof Stanek, professor of astronomy at Ohio
State. "It takes a lot of energy to shine that bright, and that energy has
to come from somewhere."
"The honest answer is
at this point that we do not know what could be the power source for
ASASSN-15lh," said Subo Dong, lead author of the Science paper and a Youth
Qianren Research Professor of astronomy at the Kavli Institute for Astronomy
and Astrophysics at Peking University. He added that the discovery "may
lead to new thinking and new observations of the whole class of superluminous
supernova."
Todd Thompson, professor of
astronomy at Ohio State, offered one possible explanation. The supernova could
have spawned an extremely rare type of star called a millisecond magnetar, a
rapidly spinning and very dense star with a very strong magnetic field.
To shine so bright, this
particular magnetar would also have to spin at least 1,000 times a second, and
convert all that rotational energy to light with nearly 100 percent efficiency,
Thompson explained. It would be the most extreme example of a magnetar that
scientists believe to be physically possible. "Given those
constraints," he said, "will we ever see anything more luminous than
this? If it truly is a magnetar, then the answer is basically no."
The Hubble Space Telescope
will help settle the question later this year, in part because it will allow
astronomers to see the host galaxy surrounding the object. If the team finds
that the object lies in the very center of a large galaxy, then perhaps it's
not a magnetar at all, and the gas around it is not evidence of a supernova,
but instead some unusual nuclear activity around a supermassive black hole.
If so, then its bright
light could herald a completely new kind of event, said study co-author
Christopher Kochanek, professor of astronomy at Ohio State and the Ohio Eminent
Scholar in Observational Cosmology.
It would be something never
before seen in the center of a galaxy.
Via DailyGalaxy
White Hole
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