The massive now-iconic object at the center of the M87 was described by scientists on April 10, 2019 as the “Gates of Hell” and the “End of Spacetime”. The Event Horizon Telescope (EHT) collaboration, who produced the first ever image of a black hole –described as “fathomless dark creations of the Universe”— an image equal to the famous “Earthrise” photo taken by Apollo 8 astronaut Bill Anders in December 1968. The EHT has released a new view of the monster elliptical galaxy located 55 million light-years away, that harbors the black hole the size of our solar system, unveiling new insights into the mystery of its magnetic fields and jets that reach at close to the speed of light beyond the galaxy.
Bright Massive Jets of Energy
The new image, reports the European Southern Observatory (ESO), captures how the iconic object looks in polarized light showing the bright jets of energy and matter that emerge from M87’s core and extend at least 5000 light-years from its center –one of the galaxy’s most mysterious and energetic features.
“As a black hole emits particles, its mass and size steadily decrease. This makes it easier for more particles to tunnel out, and so the emission will continue at an ever-increasing rate until eventually the black hole radiates itself out of existence, wrote Stephen Hawking in Black Holes and Baby Universes.
Eventual Death by Evaporation
“In the long run, every black hole in the universe will evaporate in this way.” Hawking added. “For large black holes, however, the time it will take is very long indeed; a black hole with the mass of the sun will last for about 1066 years. On the other hand, a primordial black hole should have almost completely evaporated in the almost 14 billion years that have elapsed since the big bang, the beginning of the universe as we know it. Such black holes should now be emitting hard gamma rays with an energy of about 100 million electron volts.”
First Time Measuring Polarization
This is the first time astronomers have been able to measure polarization, a signature of magnetic fields, this close to the edge of a black hole. The observations are key to explaining how the M87 galaxy is able to launch energetic jets from its core.
“We 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 Mościbrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor at Radboud University in the Netherlands.
This work is a major milestone: the polarization of light carries information that allows us to better understand the physics behind the image we saw in April 2019
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 polarized.
“This work is a major milestone: the polarization 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 Iván Martí-Vidal, also Coordinator of the EHT Polarimetry Working Group and GenT Distinguished Researcher at the University of Valencia, Spain. He adds that “unveiling this new polarized-light image required years of work due to the complex techniques involved in obtaining and analyzing the data.”
Mapping the Magnetic Field –“Eat’ Matter and Launch Powerful Jets”
Light becomes polarized when it goes through certain filters, like the lenses of polarized sunglasses, or when it is emitted in hot regions of space where magnetic fields are present. In the same way that polarized sunglasses help us see better by reducing reflections and glare from bright surfaces, astronomers can sharpen their view of the region around the black hole by looking at how the light originating from it is polarized. Specifically, polarization allows astronomers to map the magnetic field lines present at the inner edge of the black hole.
“The newly published polarized 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.
Jets Longer than the Galaxy
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 comparable in size to 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 polarized 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.
Magnetized Gas Explains What’s Seen at the Event Horizon—-The End of Time
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 magnetized gas can explain what they are seeing at the event horizon.
General relativity predicts that massive stars will collapse in on themselves when they have exhausted their nuclear fuel. Roger Penrose who won the 2020 Nobel Prize for Physics and Stephen Hawking showed that they would continue to collapse until they reached a singularity of infinite density. “This singularity,” wrote Hawking, “would be an end of time, at least for the star and anything on it. The gravitational field of the singularity would be so strong that light could not escape from the region around it but would be dragged back by the gravitational field. The region from which it is not possible to escape is called a black hole, and its boundary is called the event horizon.”
“The 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, and Coordinator of the EHT Theory Working Group.
The Planet-Sized Telescope
To observe the heart of the M87 galaxy, the collaboration linked eight telescopes around the world — including the northern Chile-based Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX), in which the European Southern Observatory (ESO) is a partner — 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.
“With ALMA and APEX, which through their southern location enhance the image quality by adding geographical spread to the EHT network, European scientists were able to play a central role in the research,” says Ciska Kemper, European ALMA Program Scientist at ESO. “With its 66 antennas, ALMA dominates the overall signal collection in polarized light, while APEX has been essential for the calibration of the image.”
“ALMA data were also crucial to calibrate, image and interpret the EHT observations, providing tight constraints on the theoretical models that explain how matter behaves near the black hole event horizon,” adds Ciriaco Goddi, a scientist at Radboud University and Leiden Observatory, the Netherlands, who led an accompanying study that relied only on ALMA observations.
“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.
Image credit: NRAO