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Mar
24
2021
17:16
11 telescopes around the world combined to research the core of a galaxy 55 million light-years away
Astronomers Image Magnetic Fields at the Edge of M87鈥檚 Black Hole
Scientists of the Event Horizon Telescope (EHT) collaboration -
among them astrophysicist Luciano Rezzolla and his team from 51猎奇
Frankfurt - have revealed today a new view of the massive object at the centre
of the M87 galaxy: how it looks in polarised light. This is the first time
astronomers have been able to measure polarisation, a signature of magnetic
fields, this close to the edge of a black hole. The observations are key to
explaining how the M87 galaxy, located 55 million light-years away, is able to
launch energetic jets from its core 鈥� jets, that are about one million light
years large.
FRANKFURT. Luciano Rezzolla, Professor of Theoretical Astrophysics at 51猎奇 Frankfurt, says: 鈥淯nderstanding what powers relativistic jets in galaxies is a long-standing open question in astrophysics. The jets in M87 are enormous and they would cover 10 per cent of our galaxy, for example. The challenging observations from the ETH telescopes, combined with the theoretical simulations carried out in Frankfurt, are now providing essential information on comparatively small length-scales: For the first time we are looking at what the magnetic field looks like that close to the black hole.
鈥淲e are now seeing the next crucial piece
of evidence to understand how magnetic fields behave around black holes, and
how activity in this very compact region of space can drive powerful jets that
extend far beyond the galaxy," says Monika Moscibrodzka, Coordinator of the EHT
Polarimetry Working Group and Assistant Professor at Radboud University in the
Netherlands.
On 10 April 2019, scientists released the
first ever image of a black hole, revealing a bright ring-like structure with a
dark central region 鈥� the black hole's shadow. Since then, the EHT collaboration
has delved deeper into the data on the supermassive object at the heart of the
M87 galaxy collected in 2017. They have discovered that a significant fraction
of the light around the M87 black hole is polarised.
鈥淭his work is a major milestone: the
polarisation of light carries information that allows us to better understand
the physics behind the image we saw in April 2019, which was not possible
before," explains Iv谩n Mart铆-Vidal, also Coordinator of the EHT Polarimetry
Working Group and GenT Distinguished Researcher at the University of Valencia,
Spain. He adds that 鈥渦nveiling this new polarised-light image required years of
work due to the complex techniques involved in obtaining and analysing the
data."
Light becomes polarised when it goes
through certain filters, like the lenses of polarised sunglasses, or when it is
emitted in hot regions of space that are magnetised. In the same way polarised
sunglasses help us see better by reducing reflections and glare from bright
surfaces, astronomers can sharpen their vision of the region around the black
hole by looking at how the light originating from there is polarised.
Specifically, polarisation allows astronomers to map the magnetic field lines
present at the inner edge of the black hole.
鈥淭he newly published polarised images are
key to understanding how the magnetic field allows the black hole to 'eat'
matter and launch powerful jets," says EHT collaboration member Andrew Chael, a
NASA Hubble Fellow at the Princeton Center for Theoretical Science and the
Princeton Gravity Initiative in the US.
The bright jets of energy and matter that
emerge from M87's core and extend at least 5000 light-years from its centre are
one of the galaxy's most mysterious and energetic features. Most matter lying
close to the edge of a black hole falls in. However, some of the surrounding
particles escape moments before capture and are blown far out into space in the
form of jets.
Astronomers have relied on different
models of how matter behaves near the black hole to better understand this
process. But they still don't know exactly how jets larger than the galaxy are
launched from its central region, which is as small in size as the Solar
System, nor how exactly matter falls into the black hole. With the new EHT
image of the black hole and its shadow in polarised light, astronomers managed
for the first time to look into the region just outside the black hole where
this interplay between matter flowing in and being ejected out is happening.
The observations provide new information
about the structure of the magnetic fields just outside the black hole. The
team found that only theoretical models featuring strongly magnetised gas can explain
what they are seeing at the event horizon.
鈥淭he observations suggest that the
magnetic fields at the black hole's edge are strong enough to push back on the
hot gas and help it resist gravity's pull. Only the gas that slips through the
field can spiral inwards to the event horizon," explains Jason Dexter,
Assistant Professor at the University of Colorado Boulder, US, and coordinator
of the EHT Theory Working Group.
To observe the heart of the M87 galaxy,
the collaboration linked eight telescopes around the world, to create a virtual
Earth-sized telescope, the EHT. The impressive resolution obtained with the EHT
is equivalent to that needed to measure the length of a credit card on the
surface of the Moon.
This allowed the team to directly observe
the black hole shadow and the ring of light around it, with the new
polarised-light image clearly showing that the ring is magnetised. The results
are published today in two separate papers in The Astrophysical Journal Letters
by the EHT collaboration. The research involved over 300 researchers from
multiple organisations and universities worldwide.
"The EHT is making rapid
advancements, with technological upgrades being done to the network and new
observatories being added. We expect future EHT observations to reveal more
accurately the magnetic field structure around the black hole and to tell us
more about the physics of the hot gas in this region," concludes EHT
collaboration member Jongho Park, an East Asian Core Observatories Association
Fellow at the Academia Sinica, Institute of Astronomy and Astrophysics in
Taipei.
Publications:
The Event Horizon Collaboration, Kazunori
Akiyama et al.: First M87 Event Horizon
Telescope Results VII: polarization of the ring. Astrophysical Journal
Letters, 910, L12 (2021) DOI 10.3847/2041-8213/abe71d (ApJL 910, L12)
The Event Horizon Collaboration: Kazunori
Akiyama et al.: First M87 Event Horizon
Telescope Results VIII: Magnetic Field Structure Near The Event Horizon.
Astrophysical Journal Letters, 910, L13 (2021) DOI 10.3847/2041-8213/abe4de
(ApJL 910, L13)
Pictures
and Videos:
(Image-Download)
A
view of the M87 supermassive black hole in polarised light: The Event Horizon Telescope (EHT) collaboration, who produced the first
ever image of a black hole released in 2019, has today a new view of the
massive object at the centre of the Messier 87 (M87) galaxy: how it looks in
polarised light. This is the first time astronomers have been able to measure
polarisation, a signature of magnetic fields, this close to the edge of a black
hole. This image shows the polarised view of the black hole in M87. The lines
mark the orientation of polarisation, which is related to the magnetic field
around the shadow of the black hole.
Credit: EHT Collaboration
(Animated GIF - Download)
Observation
and Theory Image: Transition animation showing the observed
polarization image and a best-fit theory image. Credit: S. Issaoun, M.
Mo艣cibrodzka with Polarimetry WG and OWG
(Youtube)
Zoom
into the heart of galaxy M87 鈥� The video starts
with a view on the ALMA telescope which is part of the Event Horizon Telescope,
and zooms into the heart of galaxy M87. In the core, the first image of a black
hole can be seen, the picture was produced in 2019. Then the new image follows
which shows the supermassive object in polarised light. It is the first time
that astronomers could detect polarisation as a signature of magnetic fields so
closely to the event horizon of a black hole. Credit: ESO/L. Cal莽ada, Digitized
Sky Survey 2, ESA/Hubble, RadioAstron, De Gasperin et al., Kim et al., EHT
Collaboration. Music: Niklas Falcke
(Video-Download)
Polarized
Light: Light is an oscillating electromagnetic
wave. If the waves have a preferred direction of oscillation, they are
polarized. In space, moving hot gas, or 'plasma', threaded by a magnetic field
emits polarized light. The polarized
light rays that manage to escape the pull of the black hole travel to a distant
camera. The intensity of the light rays and their direction are what EHT
collaboration observes with the Event Horizon Telescope.
Credit: 漏 EHT Collaboration and Fiks Film
(Youtube)
Black
holes are enveloped in plasma. This plasma has
magnetic fields鈥攁reas where magnetism affects how matter moves鈥攖hreaded
throughout. As the magnetic field grows stronger, it changes shape and the
polarized light EHT collaboration measures exhibits different patterns.
Credit: 漏 EHT Collaboration and
Crazybridge Studios
(Image - Download)
View
of the M87 supermassive black hole and jet in polarised light. This composite image shows three views of the central region of the
Messier 87 (M87) galaxy in polarised light. The galaxy has a supermassive black
hole at its centre and is famous for its jets that extend far beyond the
galaxy. One of the polarised-light images, obtained with the Chile-based
Atacama Large Millimeter/submillimeter Array (ALMA), shows part of the jet in
polarised light, with a size of 6000 light years from the centre of the galaxy.
The other polarised light images zoom in closer to the supermassive black hole:
the middle view covers a region about one light year in size and was obtained
with the National Radio Astronomy Observatory's Very Long Baseline Array (VLBA)
in the US. The most zoomed-in view was obtained by linking eight telescopes around
the world to create a virtual Earth-sized telescope, the Event Horizon
Telescope or EHT. This allows astronomers to see very close to the supermassive
black hole, into the region where the jets are launched. The lines mark the
orientation of polarisation, which is related to the magnetic field in the
regions imaged. The ALMA data provides a description of the magnetic field
structure along the jet. Therefore the combined information from the EHT and
ALMA allows astronomers to investigate the role of magnetic fields from the
vicinity of the event horizon (as probed with the EHT on light-day scales) to
far beyond the M87 galaxy along its powerful jets (as probed with ALMA on
scales of thousands of light-years). The values in GHz refer to the frequencies
of light at which the different observations were made. The horizontal lines
show the scale (in light years) of each of the individual images. Credit: EHT
Collaboration; ALMA (ESO/NAOJ/NRAO), Goddi et al.; VLBA (NRAO), Kravchenko et
al.; J. C. Algaba, I. Mart铆-Vidal
Further
Information:
Prof. Dr. Luciano Rezzolla
Chair of Theoretical Astrophysics
Institute
for Theoretical Physics
51猎奇 Frankfurt
Phone: +49 69 798-47871 / 47879
rezzolla@itp.uni-frankfurt.de