1st image of our galaxy’s ‘black hole heart’ unveiled

Astronomy & Astrophysics

The giant black hole is at the center of the Milky Way

The Milky Way and the location of its central black hole as viewed from the Atacama Large Millimeter/submillimeter Array. (Image credit: ESO/José Francisco Salgado (josefrancisco.org), EHT Collaboration)

Astronomers have captured the first ever image of the colossal black hole at the center of our galaxy, providing the first direct evidence of the cosmic giant’s existence.

Located 26,000 light-years away, Sagittarius A* is a gargantuan tear in space-time that is four million times the mass of our sun and 40 million miles (60 million kilometers) across. The image was captured by the Event Horizon Telescope (EHT), a network of eight synchronized radio telescopes placed in various locations around the world.

As not even light is able to escape the powerful gravitational pull of a black hole, it’s impossible to see Sagittarius A* itself except as the silhouette of a ring of fuzzy, warped light. This halo comes from the superheated, glowing matter swirling around the entrance to the cosmic monster’s maw at close to the speed of light. Once the slowly stripped and shredded plasma plunges over the black hole’s precipice, or event horizon, it is lost inside forever.

“Our results are the strongest evidence to date that a black hole resides at the centre of our galaxy,” Ziri Younsi, an astrophysicist at University College London and an EHT collaborator, said in a statement. “This black hole is the glue that holds the galaxy together. It is key to our understanding of how the Milky Way formed and will evolve in the future.”

Scientists have long thought that an enormous supermassive black hole must lurk at the center of our galaxy, its gravity tethering the Milky Way’s dust, gas, stars and planets in a loose orbit about it and causing stars closeby to circle around it rapidly. This new observation, which shows light being bent around the space-time-warping behemoth, puts their suspicions beyond all doubt.

“We were stunned by how well the ring size agreed with predictions from Einstein’s theory of general relativity,” Geoffrey Bower, an EHT collaborator and astronomer at Academia Sinica, Taipei, said in a statement. “These unprecedented observations have greatly improved our understanding of what happens at the very center of our galaxy and offer new insights on how these giant black holes interact with their surroundings.”

Einstein’s theory of general relativity describes how massive objects can warp the fabric of the universe, called space-time. Gravity, Einstein discovered, isn’t produced by an unseen force, but is simply our experience of space-time curving and distorting in the presence of matter and energy. Black holes are points in space where this warping effect becomes so strong that Einstein’s equations break down, causing not just all nearby matter but all nearby light to be sucked inside.

The Event Horizon Telescope has captured the first image of Sgr A*, the supermassive black hole at the center of our galaxy. (Image credit: EHT Collaboration)

To build a black hole, you have to start with a large star — one with a mass roughly five to 10 times that of the sun. As larger stars approach the ends of their lives, they start to fuse heavier and heavier elements, such as silicon or magnesium, inside their burning cores. But once this fusion process begins forming iron, the star is on a path to violent self-destruction. Iron takes in more energy to fuse than it gives out, causing the star to lose its ability to push out against the immense gravitational forces generated by its enormous mass. It collapses in on itself, packing first its core, and later all the matter close to it, into a point of infinitesimal dimensions and infinite density — a singularity. The star becomes a black hole, and beyond a boundary called the event horizon, nothing — not even light — can escape its gravitational pull.

Exactly how black holes may grow to become supermassive in scale is still a mystery to scientists, although observations of the early universe suggest they could balloon to their enormous sizes by snacking on dense clouds of gas and merging with other black holes.

The EHT captured the image, alongside the image of another supermassive black hole at the center of the M87 galaxy, back in 2017. The image of the M87 black hole was released in 2019, Live Science previously reported, but it took two more years of data analysis before the Milky Way one was ready.

Part of the reason behind the delay is the vastly different sizes of the two supermassive black holes, which in turn affects the speeds that their plasma clouds whirl around their centers. The M87 black hole (M87*) is roughly a thousand times bigger than Sagittarius A*, weighing in at a jaw-dropping 6.5 billion times the mass of our sun, and its hot plasma takes days or even weeks to orbit it. The plasma of Sagittarius A*, by contrast, can whip around it in mere minutes.

“This means the brightness and pattern of the gas around Sgr A* was changing rapidly as the EHT Collaboration was observing it — a bit like trying to take a clear picture of a puppy quickly chasing its tail,” Chi-kwan Chan, an EHT collaborator and astrophysicist at the University of Arizona, said in a statement.

The imaging process was made even more challenging by the Earth’s location at the edge of the Milky Way, meaning the researchers had to use a supercomputer to filter out interference from the countless stars, gas and dust clouds strewn between us and Saggitarius A*. The final result is an image which looks very similar to the 2019 snapshot of M87*, even though the two black holes are themselves vastly different in scale. This is something the researchers attribute to the startling and persisting accuracy of Einstein’s general relativity equations.

“We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes they look amazingly similar,” Sera Markoff, an EHT collaborator and astrophysicist at the University of Amsterdam in the Netherlands, said in a statement. “This tells us that general relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”

Detailed analysis of the image has already enabled scientists to make some fascinating observations into our black hole’s nature. First, it’s wonky, sitting at a 30-degree angle to the rest of the galactic disk. It also appears to be dormant, making it unlike other black holes such as M87*, which suck in burning-hot material from nearby gas clouds or stars before slingshotting it back into space at near light speeds.

The scientists will follow up with further analysis of both this image and the one of M87*, alongside capturing new and improved images. More images won’t just enable better comparisons between the black holes, but will also provide improved detail, allowing scientists to see how the same black holes change over time and what goes on around their event horizons. This could not only give us a better understanding of how our universe formed, but also help in the search for hints as to where Einstein’s equations could give way to undiscovered physics.

The researchers published their results in a series of papers in the journal The Astrophysical Journal Letters.

Originally published on Live Science
By Ben Turner
12.05.2022


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Distant ‘galaxy’ isn’t a galaxy at all — but one of the brightest pulsars ever detected

Top Science News

The pulsar is 10 times brighter than any other outside our galaxy.

Artist’s impression of newly discovered extra-galactic pulsar, PSR J0523-7125, within the Large Magellanic Cloud. (Image credit: ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav))

A speck of light that scientists once wrote off as a distant galaxy may actually be the brightest pulsar ever detected outside the Milky Way.

Named PSR J0523−7125 and located about 160,000 light-years from Earth in the Large Magellanic Cloud (a satellite galaxy that orbits the Milky Way), the newly-defined pulsar is twice as wide as any other pulsar in the region, and 10 times brighter than any known pulsar beyond our galaxy. The object is so big and bright, in fact, that researchers originally interpreted it as a faraway galaxy — however, new research published May 2 in the Astrophysical Journal Letters suggests that this is not the case.

Using the Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope in Western Australia, the study authors looked at space through a special pair of “sunglasses” that block all wavelengths of light except for a specific type of emission associated with pulsars, the highly magnetized husks of stars. When PSR J0523−7125 showed up bright and clear in the results, the team realized they weren’t looking at a galaxy at all, but at the pulsing corpse of a dead star.

“This was an amazing surprise,” lead study author Yuanming Wang, an astrophysicist at Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) said in a statement. “I didn’t expect to find a new pulsar, let alone the brightest. But with the new telescopes we now have access to, like ASKAP and its sunglasses, it really is possible.”

The MeerKAT radio telescope’s field of view without ‘sunglasses’ featuring the new pulsar (Image credit: Yuanming Wang)

Glasses on

Pulsars are highly magnetized, rapidly spinning remnants of exploded stars. As they rotate, streams of radio waves erupt from their poles, pulsing like lighthouse beams as those radio waves flash toward Earth.

The radio waves emitted by pulsars are different from many other cosmic light sources, in that they can be circularly polarized — that is, the light’s electric field can rotate in a circle as it propagates forward. This unique polarization can provide scientists with a big clue in the tricky game of distinguishing pulsars from other distant light sources. In their new study, researchers used a computer program to filter out circularly polarized light sources from an ASKAP survey of pulsar candidates.

The team found that the presumed galaxy PSR J0523−7125 was emitting circularly polarized light, meaning it is almost certainly a pulsar. And because pulsars are incredibly small — typically packing a sun’s worth of mass into a ball no wider than a city — that means the object must be much closer, and much brighter, than scientists previously thought. Indeed, if this pulsar lurks in the nearby Large Magellanic Cloud, as the researchers suspect, then it is the single brightest pulsar ever found outside the Milky Way.

The MeerKAT radio telescope’s field of view without ‘sunglasses’ featuring the new pulsar (Image credit: Yuanming Wang)

That exceptional brightness explains why the object was misidentified as a galaxy after its initial detection, the researchers said. And by filtering out circularly polarized light from future star surveys, researchers may be able to unmask even more unusual pulsars that are hiding in plain sight.

“We should expect to find more pulsars using this technique,” study co-author Tara Murphy, a radio astronomer at the University of Sydney in Australia, said in the statement. “This is the first time we have been able to search for a pulsar’s polarization in a systematic and routine way.”

Originally published on Live Science
By
12.05.2022


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