There’s a monster circling the center of our galaxy, and his portrait has finally been revealed.
Overnight, the international crew of the Event Horizon Telescope (EHT) revealed an image of superheated gas circulating and falling into Sagittarius A* or Sgr A*, the supermassive black hole at the core of the Milky Way.
It is the culmination of five years of simulations and data analysis.
And while it may look a bit like a glazed doughnut, there’s more to the new look than meets the eye.
On the one hand, it tells us that the black hole has 4 million times the mass of the Sun, a figure that physicists suspected, but which is now confirmed.
The black hole is also spinning, but it is skewed, slightly tilted toward us.
But despite this veritable goldmine of information about our galaxy’s black hole, much remains to be discovered.
What’s so special about Sgr A*?
Well, for one thing, it’s our supermassive black hole.
“It’s my home,” said Jessica Dempsey, an Australian astrophysicist and member of the EHT team.
“That’s why this one is special to a lot of people. The quest to understand what’s going on in the center of our galaxy is hundreds of years old.”
And while it may not be the largest black hole, Sgr A*’s proximity means it’s our best bet for understanding how it and its counterparts behave.
“As our instruments on the ground and in space improve our understanding, the Milky Way’s black hole will go a long way toward unraveling general relativity and how it works with quantum mechanics,” said Dr. Dempsey, former deputy director of East-Asian Observatory in Hawaii.
Understanding more about the strong heart of the Milky Way may hold clues to how our galaxy formed.
“And maybe what we can learn from Sgr A* we can start looking at… in other galaxies,” he said.
An energy inefficient giant
One of the biggest ongoing questions in the physics of black holes is exactly how they collect, ingest, and expel material orbiting them at close to the speed of light in a process known as “accretion.”
This process is fundamental to the formation and growth of planets, stars, and black holes of all sizes, throughout the universe.
Despite the bright spiral of gas and dust in the image, Sgr A* was not “eating” as much matter as the team expected.
While some black holes can be remarkably efficient at converting gravitational energy into light, Sgr A* traps and holds on to almost all of this energy.
“It converts only one part in 1,000 into light,” said Dr. Johnson.
And unlike the gigantic black hole in the galaxy M87, imaged in 2019, Sgr A* isn’t blasting a huge jet of X-ray energy into space.
But it could have a weak jet, Dr. Dempsey said, based on as-yet-unexplained quirks in how it rotates and accumulates matter.
If there is indeed a jet there, the EHT still can’t see it, but research published late last year suggests a weak jet could be presentt.
As the EHT watched the black hole, three X-ray telescopes also kept an eye on it. They detected X-ray flashes, or bursts, from Sgr A*. Signs of an airplane? Maybe.
Blank black holes to fill
James Miller-Jones, an astrophysicist at Curtin University and the International Center for Radio Astronomy Research, said measuring polarized light emitted from the black hole’s surroundings would tell us about its magnetic field.
he is something The EHT team reported, last year, on M87.
“Sgr A* appears to have a strong dynamically significant magnetic field, meaning that it is a magnetic field strong enough to affect the motion of the plasma around the black hole,” said Professor Miller-Jones.
Alister Graham, an astrophysicist at Swinburne University of Technology, was hoping to find out just how fast Sgr A* spins.
“Black holes can spin at significant fractions of the speed of light, but I felt [the EHT team] I couldn’t get an accurate reading on this.”
Another mystery yet to be solved is identifying the launch site of the plasma jets that blew up the colossal twin bubbles in the Milky Way, he added.
So how do we answer these questions? First, let’s see how astrophysicists managed to peer through a cosmic curtain of stars and gas to the black hole within our galaxy.
(Radio) lights, (telescope) camera, action!
Over a handful of nights in April 2017, when skies were clear, eight observatories from Antarctica to Europa simultaneously focused their gaze on the center of our galaxy, each tuned to record light with a wavelength of 1.3 millimeters. .
These are radio waves, invisible to our eyes, but spewed out in abundance by the incredibly hot and turbulent gas that swirls and falls into the black hole, producing the doughnut-shaped image.
Because the EHT observatories were separated by great distances, each telescope received the same radio signals from the center of the Milky Way at slightly different times.
Each data point of the radio signal was “ticked” in his telescope by an atomic clock so precise that over the course of 100 million years, it would lose just one second.
When it came time to combine the data, these timestamps allowed the physicists to synchronize the large number of signals and generate a sharper image.
This linked telescope technique, called very long baseline interferometry, essentially produces a telescope the size of the planet, and one with such high resolution that it could, in theory, detect a ping pong ball on the surface of the Moon.
So how can it be improved? It’s funny that you should ask…
Did someone say more telescopes?
The EHT has been training its radio-ready eyes on Sgr A* again, and on even more objects, in the years since its first observations in 2017.
More observatories have joined the EHT network since then, which is already making a “really huge” difference, Dr Dempsey said.
Charging
More “eyes” means the EHT can collect more light, which increases its sensitivity and ability to detect fainter features.
“The more elements we bring in, the more sensitive we become and the more confident we can be of fitting what we see… into the model,” said Dr. Dempsey.
“And the most critical part for Sgr A* is that we can make those snapshots faster.”
This means the team will eventually be able to take images on the timescales they need to produce a movie that captures dynamic features like the black hole’s rotation and the gases swirling around it.
The EHT already has spatial resolution some 5,000 times better than the Hubble Space Telescope, giving the EHT a “vast improvement” in the ability to spy objects at great distances, Professor Graham said.
But to make out finer details, we’ll need more telescopes. Though not on Earth.
“Having a radio telescope in space will offer greater gains in resolution, as will having one on the Moon,” said Professor Graham.
This is because the further apart the telescopes are from the network, the better their spatial resolution.
Plans are underway to send a 10-meter-wide radio telescope dish some 1.5 million kilometers into space, where the gravitational pull of the Earth and Sun will hold it in place.
When incorporated into the Earth-based network, the telescope, called the Millimetron Space Observatory, should give the EHT a 150-fold improvement in resolution.
The mission is led by the Russian Academy of Sciences and so far its launch is scheduled for 2030.
See in a different light
Tuning the EHT’s radio antennas to collect light of different wavelengths will also give astrophysicists different representations of the black hole.
Detection of shorter wavelengths – less than a millimeter – should provide a sharper view through the disk of our galaxy, Professor Miller-Jones said.
Comparing the brightness of the black hole’s gaseous ring at different wavelengths — for example, if it appears brighter at one wavelength than the other — could reveal some of its physical processes.
“With the next generation [EHT] facility, it will be very exciting to test our models of the environment around the black hole and what we understand about the processes of how gas flows around it,” said Professor Miller-Jones.
“All of that is going to be very, very interesting in the next few years.”
So there will undoubtedly be many more never-before-seen insights into some of the most mysterious phenomena in the universe, including our galaxy’s black hole.
“Personally, I love results that open up more questions than answers, and this [new image] is definitely one of those,” Dr. Dempsey said.
Aware , updated
Reference-www.abc.net.au