Tag: Black Holes

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Universe Today

Telescope tracks fireworks around our galaxy’s black hole

Flares in disk surrounding Milky Way's central black hole
An illustration shows hot spots in the disk swirling around the Milky Way's central black hole. (Credit: NASA, ESA, CSA, Ralf Crawford / STScI)

The supermassive black hole at the center of our Milky Way galaxy may not be as voracious as the gas-gobbling monsters that astronomers have seen farther out in the universe, but new findings from NASA’s James Webb Space Telescope reveal that its surroundings are flaring with fireworks.

JWST’s readings in two near-infrared wavelengths have documented cosmic flares that vary in brightness and duration. Researchers say the accretion disk of hot gas surrounding the black hole, known as Sagittarius A*, throws off about five or six big flares a day, and several smaller bursts in between. The observations are detailed today in The Astrophysical Journal Letters.

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Universe Today

Scientists map magnetism around our galaxy’s black hole

Polarization image of Milky Way's supermassive black hole from EHT
An image from the Event Horizon Telescope shows lines of polarization around the Milky Way's central black hole. (Credit: EHT Collaboration)

Fresh imagery from the Event Horizon Telescope traces the lines of powerful magnetic fields spiraling out from the edge of the supermassive black hole at the center of our Milky Way galaxy, and suggests that strong magnetism may be common to all supermassive black holes.

The newly released image showing the surroundings of the black hole known as Sagittarius A* — which is about 27,000 light-years from Earth — is the subject of two studies published today in The Astrophysical Journal Letters. This picture follows up on an initial picture issued in 2022. Both pictures rely on radio-wave observations from the Event Horizon Telescope’s network of observatories around the world.

Sagittarius A* wasn’t the first black hole whose shadow was imaged by the EHT. Back in 2019, astronomers showed off a similar picture of the supermassive black hole at the center of the galaxy M87, which is more than a thousand times bigger and farther away than the Milky Way’s black hole.

In 2021, the EHT team charted the magnetic field lines around M87’s black hole by taking a close look at the black hole in polarized light, which reflects the patterns of particles whirling around magnetic field lines. Researchers used the same technique to determine the magnetic signature of Sagittarius A*, or Sgr A* for short.

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GeekWire

Scientists find evidence of a gravitational wave ‘hum’

Illustration: Ripples in spacetime caused by gravitational waves
Scientists monitor how ripples in spacetime affect the timing of signals from pulsars. (Credit: Aurore Simonnet for NANOGrav Collaboration)

Astrophysicists have found the best evidence yet for a low-frequency “hum” of gravitational waves rippling through the cosmos, based on 15 years’ worth of ultra-precise measurements checking the timing of radio pulses from distant stars.

The evidence, newly published in the Astrophysical Journal Letters, comes from several teams of researchers working in the U.S. and Canada as well as Europe, India, Australia and China.

The teams monitored radio emissions from a total of 115 ultra-dense, spinning stars known as pulsars. Nearly 70 of those pulsars were observed by the North American Nanohertz Observatory for Gravitational Waves, known as NANOGrav.

“This is key evidence for gravitational waves at very low frequencies,” Vanderbilt University’s Stephen Taylor, who co-led the search and is the current chair of the NANOGrav Collaboration, said today in a news release. “After years of work, NANOGrav is opening an entirely new window on the gravitational-wave universe.”

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GeekWire

Gravitational-wave sleuths look for more cosmic crashes

Specialist checks beam alignment at LIGO
A specialist checks the alignment of a test beam at the Laser Interferometer Gravitational-wave Observatory. (NSF Photo)

After three years of upgrading and waiting, due in part to the coronavirus pandemic, the Laser Interferometer Gravitational-wave Observatory has officially resumed its hunt for the signatures of crashing black holes and neutron stars.

“Our LIGO teams have worked through hardship during the past two-plus years to be ready for this moment, and we are indeed ready,” Caltech physicist Albert Lazzarini, the deputy director of the LIGO Laboratory, said in a news release.

Lazzarini said the engineering tests leading up to today’s official start of Observing Run 4, or O4, have already revealed a number of candidate events that have been shared with the astronomical community.

“Most of these involve black hole binary systems, although one may include a neutron star,” he said. “The rates appear to be consistent with expectations.”

One such event, called S230518h, was detected last week. Researchers say that if they can confirm the data, the event was most likely caused by the merger of a faraway black hole and a neutron star.

The twin LIGO gravitational-wave detectors at Hanford, Wash., and Livingston, La., will be joined for O4 by the Virgo detector in Italy as well as the KAGRA observatory in Japan. Virgo is scheduled to take part in the run starting later this year. KAGRA will parallel LIGO’s observations for the next month, take a break for some upgrades, and then rejoin the run.

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Universe Today

AI produces a sharper image of M87’s black hole

Three views of M87's black hole
Three views of a black hole, from left to right: Event Horizon Telescope's original image, PRIMO reconstruction and image blurred to match EHT's resolution. (Credit: Lia Medeiros et al. / ApJL, 2023)

Astronomers have used machine learning to sharpen up the Event Horizon Telescope’s first picture of a black hole — an exercise that demonstrates the value of artificial intelligence for fine-tuning cosmic observations.

The image should guide scientists as they test their hypotheses about the behavior of black holes, and about the gravitational rules of the road under extreme conditions.

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Cosmic Space

Scientists say we were caught in a black hole’s bull’s-eye

Illustration: Tidal disruption event sparked by black hole
Artwork depicts a tidal disruption event. (Carl Knox / OzGrav / ARC Centre of Excellence for Grav. Wave Discovery, Swinburne Univ. of Tech.)

Nine months ago, astronomers observed a flash that they said came from a mysterious object that seemed to flare with the brilliance of a quadrillion suns, located 8.5 billion light-years from Earth.

Now they say they’ve figured out what that object was.

In a pair of studies published by Nature and Nature Astronomy, researchers report that the event was probably sparked when a supermassive black hole suddenly consumed a nearby star. The event’s violent energy was released in the form of a relativistic jet of blazing-hot material that headed in Earth’s direction.

The jet didn’t do us any damage. But its bull’s-eye directionality produced a phenomenon called “Doppler boosting,” also known as the headlight effect. That made the jet’s flash look brighter than it would have if the jet went in a different direction.

Scientists say the flash, which was designated AT2022cmc when it was detected by the Zwicky Transient Facility in February, is only the fourth known example of a Doppler-boosted tidal disruption event.

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Cosmic Space

See our galaxy’s black hole — and hear what’s next

Sagittarius A* black hole shadow
This is the first image of Sagittarius A*, the supermassive black hole at the center of our galaxy. (EHT Collaboration via NSF)

After years of observation and weeks of rumor-mill rumblings, astronomers today unveiled their first image of the supermassive black hole at the center of our own Milky Way galaxy, Sagittarius A*.

Technically, the picture from the Event Horizon Telescope project doesn’t show light from the black hole itself. After all, a black hole is a gravitational singularity so dense that nothing, not even light, can escape its grip. Rather, the picture shows the “shadow” of a black hole, surrounded by the superheated, glowing gas that surrounds it.

And technically, the picture may not match what folks might see with their own eyes up close. Rather, the readings come from eight observatories around the world that combined their observations in radio wavelengths.

Nevertheless, the new view of Sagittarius A*, or Sgr A* for short (pronounced “sadge-ay-star”), serves to confirm in graphic terms what astronomers have long suspected: that our galaxy, like many others, has a supermassive black hole at its heart.

Today’s revelations follow up on the Event Horizon Telescope’s first-ever black hole image, which was released in 2019 and showed the supermassive black hole at the center of M87, an elliptical galaxy about 55 million light-years away.

Sgr A* is much closer — a mere 27,000 light-years from Earth, in the constellation Sagittarius. But there’s nothing to fear from this black hole: It’s relatively quiescent, in contrast to the galaxy-gobbling behemoths that are standard science-fiction fare.

Our galaxy’s black hole is thought to hold the mass of 4 million suns within an area that’s roughly as big around as Mercury’s orbit. Checking those dimensions against the image data serves as a test of relativity theory. Spoiler alert: Albert Einstein was right … again.

“We were stunned by how well the size of the ring agreed with predictions from Einstein’s theory of general relativity,” EHT project scientist Geoffrey Bower said in a news release. “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.”

The EHT’s findings about Sgr A* are the subject of a special issue of The Astrophysical Journal Letters — and to whet your appetite for all that reading material, here are three videos that summarize the past, present and future of black hole imaging:

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GeekWire

Student wins top prize for gravitational wave work

Christine Ye
Eastlake High School senior Christine Ye focused on gravitational waves in her research. (UW Bothell Photo)

Christine Ye, a senior at Eastlake High School in Sammamish, Wash., has won the top award in the nation’s oldest and most prestigious competitions for science students, thanks to her research into the mysteries of black holes and neutron stars.

“I’m totally in shock,” the 17-year-old told me after winning the $250,000 first-place award in the 2022 Regeneron Science Talent Search. “It feels amazing.”

Ye was among 40 finalists honored on March 15 in Washington, D.C., during a live-streamed ceremony that was emceed by “Saturday Night Live” cast member Melissa Villaseñor. More than $1.8 million in all was awarded to the finalists, who were evaluated on the basis of their projects’ scientific rigor and their potential to become scientific leaders.

Ye’s award-winning research is based on an analysis of readings from the Laser Interferometer Gravitational-wave Observatory, and addresses one of LIGO’s most puzzling observations.

In 2019, researchers at LIGO and at Europe’s Virgo gravitational-wave observatory detected ripples in spacetime that were caused by the collision of a black hole and a mystery object that was 2.6 times as massive as our sun. The object’s size fell into a “mass gap” between the heaviest known neutron star and the lightest known black hole.

The analysis conducted by Ye and her co-author, Northwestern University postdoctoral fellow Maya Fishbach, determined that rapidly spinning neutron stars could get as massive as the mystery object. Their study will be the subject of a presentation next month in New York at a meeting of the American Physical Society.

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Cosmic Space

Confirmed! Black holes and neutron stars collide

Black hole / neutron star merger
Artwork shows a black hole and a neutron star circling toward a merger. (Credit: Carl Knox / OzGrav / Swinburne U.)

Gravitational-wave astronomers are confident that they’ve filled out their repertoire of cataclysmic collisions, thanks to the detection of two cosmic crashes that each involved a black hole and a neutron star.

Over the past five years, astronomers have used the twin LIGO gravitational-wave detectors in Washington state and Louisiana, plus the Virgo detector in Italy, to pick up signals from more than 50 violent mergers of black holes with black holes, or neutron stars with neutron stars.

In 2019, the astronomers picked up readings from two events that might have been caused by hot black-hole-on-neutron-star action. But one of those detections, on April 26, 2019, could plausibly have been nothing more than noise in the detectors. The other event, on Aug. 14, 2019, involved a crash between a black hole and an object that was either the heaviest known neutron star or the lightest known black hole. The gravitational-wave hunters couldn’t say definitively which.

In contrast, astronomers leave little doubt that the gravitational waves sparked by two separate events in January 2020 were thrown off by the merger of a black hole and a neutron star. They lay out their evidence in a paper published today by The Astrophysical Journal Letters.

“With this new discovery of neutron star-black hole mergers outside our galaxy, we have found the missing type of binary. We can finally begin to understand how many of these systems exist, how often they merge, and why we have not yet seen examples in the Milky Way,” Astrid Lamberts, a member of the Virgo collaboration who works at the Observatoire de la Côte d’Azur in France, said in a news release.

There’s still some mystery surrounding the detections.

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Fiction Science Club

The meaning of life, death … and black holes

M87 black hole in polarized light
This view of the M87 supermassive black hole in polarized light highlights the signature of magnetic fields. (Credit: EHT Collaboration)

Why are black holes so alluring?

You could cite plenty of reasons: They’re matter-gobbling monsters, making them the perfect plot device for a Disney movie. They warp spacetime, demonstrating the weirdest implications of general relativity. They’re so massive that inside a boundary known as the event horizon, nothing — not even light — can escape its gravitational grip.

But perhaps the most intriguing feature of black holes is their sheer mystery. Because of the rules of relativity, no one can report what happens inside the boundaries of a black hole.

“We could experience all the crazy stuff that’s going on inside a black hole, but we’d never be able to tell anybody,” radio astronomer Heino Falcke told me. “We want to know what’s going on there, but we can’t.”

Falcke and his colleagues in the international Event Horizon Telescope project lifted the veil just a bit two years ago when they released the first picture ever taken of a supermassive black hole’s shadow. But the enduring mystery is a major theme in Falcke’s new book about the EHT quest, “Light in the Darkness: Black Holes, the Universe, and Us” — and in the latest installment of the Fiction Science podcast, which focuses on the intersection of fact and science fiction.

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