Black holes simply like engulfing themselves in brightness, which is amazing considering that they cannot be seen to generate any light.
Supermassive black holes in reality produce some of the
universe's brightest light. The matter surrounding black holes, which actively
slurp down enormous amounts of matter from their immediate surroundings, is
what causes the problem, not the black holes themselves.
Blazar galaxies are some of these hot, swirling,
maelstrom-like masses that are brightest. They emit electromagnetic radiation
at energies that are difficult to comprehend, and in addition to glowing with
the heat of a swirling coat, they can also channel material into
"blazing" beams that travel through space.
The mechanism causing the extraordinary high-energy light
that reached Earth billions of years ago has finally been identified by
scientists: shocks in the black hole's jets that cause particles to travel at incredible
speeds.
According to astronomer Yannis Liodakis of the Finnish Centre
for Astronomy with ESO, "We have solved a 40-year-old mystery."
"The picture they painted was clear when we finally had all the pieces of
the puzzle,"
A supermassive black hole is the centre of the vast majority
of galaxies in the universe. These enormous celestial bodies are located in the
galactic core, where they occasionally perform relatively little work (like
Sagittarius A*, the Milky Way's central black hole), and occasionally perform a
great deal.
That action entails the accumulation of matter. A huge cloud
forms an equatorial disc that encircles the black hole like water does a drain.
This material heats up and shines brightly across a range of wavelengths due to
the frictional and gravitational interactions at work in the extreme space
surrounding a black hole. That is one place where a black hole gets its light.
The other, which also occurs in blazars, is a pair of
material jets that are fired perpendicular to the disc from the polar regions
outside the black hole. These jets are believed to be made of material from the
inner rim of the disc that, rather than collapsing into the black hole, is
propelled to the poles by acceleration along lines of the external magnetic field
at speeds that are almost as fast as light.
These jets must be almost directly pointed at the observer
for a galaxy to be categorised as a blazar. We are that on Earth. They emit
light across the electromagnetic spectrum, including high-energy gamma- and
X-rays, as a result of the extreme particle acceleration.
For many years, it has been unclear exactly how this jet
accelerates the particles to such high speeds. But now, scientists have the
solution thanks to the Imaging X-ray Polarimetry Explorer (IXPE), a potent new
X-ray telescope that was launched in December 2021. It is the first space
telescope to show how X-rays are oriented, or polarized.
According to astronomer Immacolata Donnarumma of the Italian
Space Agency, "the first X-ray polarisation measurements of this class of
sources allowed, for the first time, a direct comparison with the models
developed from observing other frequencies of light, from radio to very
high-energy gamma rays."
IXPE was pointed at the Markarian 501 blazar, which is 460 million
light-years away in the constellation of Hercules and is the brightest
high-energy object in our sky. The telescope recorded data on the X-ray light
emitted by the blazar's jet for a total of six days in March 2022.
IXPE is seen viewing Markarian 501 in this picture, with
light progressively losing energy as it gets further away from the shock front.
The light from other wavelength ranges, from radio to
optical, was being measured simultaneously by other observatories, which were
previously the only sources of information for Markarian 501.
The group picked up on a strange change in the X-ray light
right away. Compared to the lower-energy wavelengths, its polarisation was
noticeably more twisted. And radio frequencies were less polarised than optical
light.
However, the polarization's orientation was consistent across
all wavelengths and coincided with the jet's path. The team discovered that
this is in line with models in which shocks in the jets result in shockwaves
that give the jet additional acceleration along its length. This acceleration
is greatest right before the shock, which results in X-radiation. The particles
lose energy as they travel further along the jet, producing lower-energy
optical and later radio emission with less polarization.
According to astronomer Alan Marscher of Boston University,
"when the shock wave penetrates the region, the magnetic field increases
stronger and the energy of particles gets higher." "The substance
creating the shock wave's motion energy is where the energy originates
from."
The cause of the shocks is unknown, but one potential
mechanism is that faster jet material catches up to slower-moving clumps,
causing collisions. Future investigation might support this theory.
This study adds a significant piece to the puzzle because
blazars are among the Universe's most potent particle accelerators and one of
the best laboratories for studying extreme physics.
In the future, observations of Markarian 501 will continue,
and IXPE will be directed to other blazars to see if similar polarisation can
be found.
The study was released in the journal Nature Astronomy.
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