The first-ever photo of a
black hole rocked the world in 2019, when the Event Horizon Telescope, or EHT,
published an image of the supermassive black hole at the center of the galaxy
M87, also known as Virgo A or NGC 4486, located in the constellation of Virgo.
This black hole is surprising scientists again with a teraelectronvolt
gamma-ray flare — emitting photons billions of times more energetic than
visible light. Such an intense flare has not been observed in over a decade,
offering crucial insights into how particles, such as electrons and positrons,
are accelerated in the extreme environments near black holes.
The jet coming out of the center of M87
is seven orders of magnitude — tens of millions of times — larger than the
event horizon, or surface of the black hole itself. The bright burst of
high-energy emission was well above the energies typically detected by radio
telescopes from the black hole region. The flare lasted about three days and
probably emerged from a region less than three light-days in size, or a little
under 15 billion miles.
A gamma ray is a packet of
electromagnetic energy, also known as a photon. Gamma rays have the most energy
of any wavelength in the electromagnetic spectrum and are produced by the
hottest and most energetic environments in the universe, such as regions around
black holes. The photons in M87’s gamma ray flare have energy levels up to a
few teraelectronvolts. Teraelectronvolts are used to measure the energy in
subatomic particles and are equivalent to the energy of a mosquito in motion.
This is a huge amount of energy for particles that are many trillion times
smaller than a mosquito. Photons with several teraelectronvolts of energy are
vastly more energetic than the photons that make up visible light.
As matter falls toward a black hole, it
forms an accretion disk where particles are accelerated due to the loss of
gravitational potential energy. Some are even redirected away from the black
hole’s poles as a powerful outflow, called “jets,” driven by intense magnetic
fields. This process is irregular, which often causes a rapid energy outburst
called a “flare.” However, gamma rays cannot penetrate Earth’s atmosphere.
Nearly 70 years ago, physicists discovered that gamma rays can be detected from
the ground by observing the secondary radiation generated when they strike the
atmosphere.
“We still don’t fully understand how
particles are accelerated near the black hole or within the jet,” said Weidong
Jin, a postdoctoral researcher at UCLA and a corresponding author of a paper describing the findings published by an
international team of authors in Astronomy & Astrophysics. “These particles
are so energetic, they’re traveling near the speed of light, and we want to
understand where and how they gain such energy. Our study presents the most
comprehensive spectral data ever collected for this galaxy, along with modeling
to shed light on these processes.”
Jin contributed to analysis of the
highest energy part of the dataset, called the very-high-energy gamma rays,
which was collected by VERITAS — a ground-based gamma-ray instrument operating
at the Fred Lawrence Whipple Observatory in southern Arizona. UCLA played a
major role in the construction of VERITAS — short for Very Energetic
Radiation Imaging Telescope Array System — participating in the development of
the electronics to read out the telescope sensors and in the development of
computer software to analyze the telescope data and to simulate the telescope
performance. This analysis helped detect the flare, as indicated by large
luminosity changes that are a significant departure from the baseline
variability.
More than two dozen high-profile ground-
and space-based observational facilities, including NASA’s Fermi-LAT, Hubble
Space Telescope, NuSTAR, Chandra and Swift telescopes, together with the
world’s three largest imaging atmospheric Cherenkov telescope arrays (VERITAS, H.E.S.S.
and MAGIC) joined this second EHT and multi-wavelength campaign in 2018. These
observatories are sensitive to X-ray photons as well as high-energy and
very-high-energy gamma-rays, respectively.
One of the key datasets used in this
study is called spectral energy distribution.
“The spectrum describes how energy from
astronomical sources, like M87, is distributed across different wavelengths of
light,” Jin said. “It’s like breaking the light into a rainbow and measuring
how much energy is present in each color. This analysis helps us uncover the
different processes that drive the acceleration of high-energy particles in the
jet of the supermassive black hole.”
Further analysis by the paper’s authors
found a significant variation in the position and angle of the ring, also
called the event horizon, and the jet position. This suggests a physical
relationship between the particles and the event horizon, at different size
scales, influences the jet’s position.
“One of the most striking features of
M87’s black hole is a bipolar jet extending thousands of light years from the
core,” Jin said. “This study provided a unique opportunity to investigate the
origin of the very-high-energy gamma-ray emission during the flare, and to
identify the location where the particles causing the flare are being
accelerated. Our findings could help resolve a long-standing debate about the
origins of cosmic rays detected on Earth.”
Source: https://newsroom.ucla.edu/releases/astrophysicists-capture-huge-gamma-ray-flare-supermassive-black-hole-m87
Journal article: https://www.aanda.org/articles/aa/full_html/2024/12/aa50497-24/aa50497-24.html
Image Credit: EHT Collaboration,
Fermi-LAT Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS
Collaboration, EAVN Collaboration
Light curve of the gamma-ray flare (bottom) and collection of quasi-simulated images of the M87 jet (top) at various scales obtained in radio and X-ray during the 2018 campaign. The instrument, the wavelength observation range and scale are shown at the top left of each image.
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