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Cosmic Space

Black hole’s shadow boosts the case for relativity

The first-ever picture of a black hole is the gift that keeps on giving — in the form of new insights into the dynamics behind the mysterious phenomenon and new evidence that Albert Einstein was right.

The validity of Einstein’s theory of general relativity has been proven time and time again over the course of the past century. But physicists keep coming up with new ideas for tweaking the theory’s equations in unorthodox ways.

To figure out how much leeway there could be for variations on Einstein’s theme, researchers took a closer look at the supermassive black hole at the center of the galaxy M87.

M87’s black hole, which lies about 55 million light-years from Earth, was featured in a history-making close-up last year, produced by a radio astronomy collaboration known as the Event Horizon Telescope. The achievement is likely to win the EHT collaboration a Nobel Prize as soon as next week.

The team behind the relativity-checking research, published this week in Physical Review Letters, measured the size of the black hole’s shadow — that is, the dark central region from which light rays can’t escape, due to the gravitational pull of a singularity that’s 6.5 billion times as massive as our sun.

The predicted size of the shadow could vary, depending on which theory of gravity you go with. But in M87’s case, the size matched up precisely with Einstein’s theory.

“Using the gauge we developed, we showed that the measured size of the black hole shadow in M87 tightens the wiggle room for modifications to Einstein’s theory of general relativity by almost a factor of 500, compared to previous tests in the solar system,” the University of Arizona’s Feryal Özel, a senior member of the EHT collaboration, said in a news release.

“Many ways to modify general relativity fail at this new and tighter black hole shadow test,” Özel said.

The Event Horizon Telescope’s findings add to a bonanza of black hole data from the Laser Interferometer Gravitational-wave Observatory, or LIGO, and Europe’s VIRGO detector.

“Together with gravitational-wave observations, this marks the beginning of a new era in black hole astrophysics,” said lead study author Dimitrios Psaltis, a University of Arizona astronomer who recently finished his stint as the EHT collaboration’s project scientist.

And the EHT isn’t stopping with last year’s image. Just last month, the collaboration unveiled a “movie” that shows a wobbling pattern of emissions from the surroundings of M87’s black hole. The analysis of black hole dynamics over time, published in The Astrophysical Journal, was created by feeding more than a decade’s worth of observations into a computer model.

Eight observatories around the world contributed to the initial round of observations for the Event Horizon Telescope project. For the EHT’s next campaign in 2021, there’ll be three more observatories on the case, in Arizona, Greenland and France.

The added capacity should result in higher-fidelity images — not only of M87’s black hole, but also of Sagittarius A*, the supermassive black hole at the center of our own Milky Way galaxy.

Up-close views of black holes could well shine a light on another prediction made by general relativity, known as the no-hair theorem. This theorem states that the characteristics of black holes are completely determined by their mass, spin and electrical charge.

If the theorem is correct, all black holes with the same values for those three attributes would be identical to each other. Any other distinguishing characteristics for black holes and their history — their “hair,” metaphorically speaking — would disappear forever inside the black hole’s event horizon.

In a theoretical paper that was published months after the death of British physicist Stephen Hawking, he and three co-authors argued that black holes might be surrounded by a distinctive kind of “soft hair” that’s left behind as they evolve. This would have deep implications for general relativity, and for a long-running, almost metaphysical debate over what happens when something falls into a black hole.

Was Einstein right, or was Hawking? Thanks to gravitational-wave detectors and the Event Horizon Telescope, we could well find out.

Flash interactive: Putting Einstein to the test
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Cosmic Space

Black hole crash creates LIGO’s biggest ‘bang’

Scientists say the merger of two black holes that occurred when the universe was half its current age has created the most massive source of gravitational waves ever observed.

After traveling billions of light-years, the disturbance in spacetime was picked up on May 21, 2019, by the Laser Interferometer Gravitational-Wave Observatory, also known as LIGO, and the Virgo gravitational-wave detector in Italy. The unusual event and its implications are described in papers published today by Physical Review Letters and the Astrophysical Journal Letters.

“This doesn’t look much like a chirp, which is what we typically detect,” Nelson Christensen, an astrophysicist at the French National Center for Scientific Research, said in a news release. “This is more like something that goes ‘bang,’ and it’s the most massive signal LIGO and Virgo have seen.”

Christensen and his colleagues say the signal, known as GW190521, appears to have come from the violent collision of two spinning black holes that were about 85 and 66 times as massive as our sun.

The merger created an even bigger black hole that’s about 142 times as massive as the sun. It also released the equivalent of eight solar masses in the form of gravitational-wave energy, in accordance with Albert Einstein’s E=mc2 formula, the scientists said.

GW190521 not only ranks as the biggest bang recorded since LIGO made its initial, Nobel-winning gravitational-wave detection in 2015. It also counts as LIGO’s first detection of a mysterious object known as an intermediate-mass black hole.

For decades, physicists have been fleshing out their theories regarding the nature and origin of black holes — concentrations of matter so massive and compact that nothing, not even light, can escape their gravitational grip.

Some black holes are thought to be created when stars up to 130 times as massive as our sun run out of their fusion fuel and collapse inward, producing black holes as big as 65 solar masses. There are also scenarios in which stars that weigh more than 200 solar masses can collapse into black holes in the range of 120 solar masses.

A completely different process leads to the creation of monster black holes at the centers of galaxies (including our own galaxy). Such supermassive black holes are at least 1,000 times as massive as the sun.

Not that long ago, scientists thought the physics behind gravitational collapse ruled out the creation of black holes between 65 and 120 solar masses. Instead, the collapse of midsize stars was thought to produce instability through the creation of electron-antielectron pairs — and as a result, the stars were supposed to blow themselves completely apart.

Now, the fact that one of the black holes involved in last year’s smashup was measured at 85 solar masses is complicating claims for the existence of a pair instability mass gap.

“The fact that we’re seeing a black hole in this mass gap will make a lot of astrophysicists scratch their heads and try to figure out how these black holes are made,” said Christensen, who is the director of the Artemis Laboratory at the Nice Observatory in France.

The authors of the paper published in the Astrophysical Journal Letters have already come up with one possibility: Perhaps the midsize black hole was not directly produced by a stellar collapse, but instead by an earlier merger of smaller black holes — just the sort of merger that LIGO and Virgo have been detecting over the past five years.

“This event opens more questions than in provides answers,” said Caltech physicist Alan Weinstein, a member of the LIGO collaboration. “From the perspective of discovery and physics, it’s a very exciting thing.”

Weinstein cautioned that there’s still some uncertainty about the current explanation for GW190521.

“Since we first turned on LIGO, everything we’ve observed with confidence has been a collision of black holes or neutron stars,” he said. “This is the one event where our analysis allows the possibility that this event is not such a collision.  Although this event is consistent with being from an exceptionally massive binary black hole merger, and alternative explanations are disfavored, it is pushing the boundaries of our confidence. And that potentially makes it extremely exciting.”

Further observations from LIGO and Virgo could turn up something completely new in the gravitational-wave menagerie — for example, evidence for the creation of primordial cosmic strings.

The LIGO project is funded by the National Science Foundation and operated by Caltech and MIT. It relies on two gravitational-wave detectors that have been built at Hanford, Wash., and at Livingston, La., with about 2,000 miles of separation to provide a double-check on the detectors’ results.

Each detector consists of an L-shaped network of tunnels, measuring 2.5 miles on a side, with laser beams reflected back and forth within the tunnels. Gravitational waves from far-off cataclysms disturb the fabric of spacetime ever so slightly — but the detectors are sensitive enough to pick up such disturbances to within the width of a proton.

Europe’s Virgo detector, designed according to a similar scheme, provides further verification for LIGO’s gravitational-wave data and makes it easier to triangulate on the sources of the waves.

In the case of GW190521, the waves are thought to have been thrown off by a source that’s now roughly 17 billion light-years (5 gigaparsecs) away from us — at a time when the universe was about half its current age of 13.8 billion years. That makes it one of the most distant gravitational-wave sources detected so far.

Because light travels at a finite speed, it may seem counterintuitive for a signal that was sent out 7 billion years ago to be received from an object that’s 17 billion light-years away.

But in an email exchange, Weinstein told me there’s a relatively simple explanation for the seeming mismatch. “The universe has been expanding since the gravitational waves were emitted,” he wrote. “So physical distances are tricky to interpret in an expanding universe, and must be treated with care.”

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GeekWire

Gravitational waves point to cosmic conundrum

Telltale ripples in the fabric of spacetime have revealed the existence of a cosmic object that scientists can’t definitively classify.

Whatever it is, the object was engulfed suddenly by a black hole weighing 23.2 times the mass of our sun, 800 million light-years away. The gravitational waves thrown off by that violent merger were picked up last August by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory, or LIGO, and by the Virgo gravitational-wave detector in Italy.

The gravitational-wave patterns revealed that the smaller object was 2.6 times as massive as our sun. And that’s where the classification problem arises.

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GeekWire

Year in Science: Sights never seen before 2019

Black hole
This image from the Event Horizon Telescope shows the supermassive black hole in the elliptical galaxy M87, surrounded by superheated material. (EHT Collaboration)

What will people remember about the year 2019 in the year 3019? Just as they’re likely to recall 1969 as the year humans first walked on the moon, they might well hold up the first portrait of a black hole as this year’s most memorable achievement.

By that measure, there’s little question that the Event Horizon Telescope’s radio view of M87’s supermassive black hole, 55 million light-years from Earth, ranks as the year’s top science story. “These are just singular moments in history,” White House science adviser Kelvin Droegemeier told me in April when the image was unveiled in Washington, D.C. “We as humans need this.”

The best part is that the story isn’t over.

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Black hole portrait wins Breakthrough Prize

Black hole
This image from the Event Horizon Telescope shows the supermassive black hole in the elliptical galaxy M87, surrounded by superheated material. (EHT Collaboration)

What’s $3 million divided by 347? That’s the math problem to be solved by the physicists on the Event Horizon Telescope team, who won one of the top awards in the Breakthrough Prize program for snapping the first picture showing the dark maw of a supermassive black hole.

Now in its eighth year, the “Oscars of Science” honor achievements in fundamental physics, life sciences and mathematics. Past winners have included the late British physicist Stephen Hawking and the teams behind the Large Hadron Collider (for discovering the Higgs Boson), the Laser Interferometer Gravitational-wave Observatory (a.k.a. LIGO) and the Wilkinson Microwave Anisotropy Probe (for producing a map of the Big Bang’s afterglow).

The lineup of backers is almost as well known as the lineup of laureates: It’s the brainchild of Israeli-Russian billionaire Yuri Milner and his wife Julia, with Google co-founder Sergei Brin, Facebook CEO Mark Zuckerberg and Priscilla Chan, Ma Huateng and Anne Wojcicki also serving as sponsors.

Each Breakthrough Prize carries a $3 million award, to be shared by the recipients. That calls for some arithmetic when you’re talking about the more than 1,000 scientists behind LIGO’s award-winning detection of a black hole merger.

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It’s a double whammy of gravitational waves!

Image: Black hole merger
A computer simulation shows two black holes shortly before they merge into one. (Credit: SXS)

Two detections of gravitational waves, separated by a mere 21 minutes, set off a flurry of excitement among astronomers today.

Was it a binary black-hole merger? A double observation of a single black-hole merger, created by gravitational lensing effects? A glitch affecting the analytical systems at the world’s gravitational-wave detectors? Or merely a coincidence of cosmic proportions?

“This is a genuine ‘Uh, wait, what?’ We’ve never seen that before…….’ moment in gravitational wave astronomy,” Robert Rutledge, a physicist at McGill University, tweeted today. “If you’d like to see how double-checks and confirmations and conclusions occur – pay attention, in real time. Happening now.”

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Did a black hole just gobble up a neutron star?

Neutron star and black hole illustration
An artist’s conception shows a neutron star swirling around a black hole. (OzGrav ARC Centre of Excellence Illustration via Australian National University / Carl Knox)

The Laser Interferometer Gravitational-Wave Observatory, or LIGO,  has detected mergers of black holes, and even a couple of neutron star smash-ups. But it hasn’t yet confirmed the signature of a black hole gobbling a neutron star.

That could soon change.

Over the past week, physicists have been buzzing over an Aug. 14 detection made by the twin LIGO detectors in Hanford, Wash., and Livingston, La., as well as by the European Virgo gravitational-wave detector in Italy. Those L-shaped facilities monitor ever-so-slight fluctuations in laser beams to look for wobbles in spacetime caused by passing gravitational waves.

The types of waves that LIGO and Virgo detect are given off only by violent cosmic events such as supernova explosions and cataclysmic collisions. LIGO’s first black hole detection, made in 2015, earned the Nobel Prize in physics two years later. More such detections have been made since then.

Detecting the first neutron star merger, and matching that event up with multispectral observations from a wide array of telescopes, marked another milestone in 2017. Neutron stars are the super-dense stellar cores that are left behind when stars bigger than our sun burn out and collapse.

Picking up on the collision of a neutron star and a black hole would complete a gravitational-wave trifecta. LIGO’s team thought they might have detected such a smash-up back in April, but the signal was weak and couldn’t be confirmed.

Astronomers say the Aug. 14 detection, known as S190814bv and traced to a source roughly 900 million light-years away, could be the one.

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Cosmic Space

50 shades of black holes for 17 years of Cosmic Log

This week marks 17 years since Cosmic Log was founded, and to celebrate the occasion, here’s the text of a talk I gave this month at Theatre Off Jackson for Infinity Box Theatre’s “Centrifuge” production of science-oriented one-act plays. My talk, titled “Fifty Shades of Black Holes,” set the scene for a three-actor drama about a black hole expedition. To take a walk down Cosmic Log’s memory lane, check out our archives.

I bet you never thought you’d be learning about black holes, the holographic principle and digital consciousness theory tonight. But you’ll be getting a taste of all of that in just a few minutes, in Harold Taw’s play about the Primrose Protocol.

My name is Alan Boyle. I’m the aerospace and science editor at GeekWire, and you can consider this a prologue to set the scientific scene.

I actually write about black holes every so often – for example, I was in Washington, D.C., last month for the unveiling of the first-ever image of a supermassive black hole. This one is in M87, a galaxy that’s about 55 million light-years away. But our own Milky Way galaxy also has a black hole at its center, a mere 26,000 light-years away.

If you’re up on your science fiction, you probably know that a black hole is a gravitational singularity so dense that nothing, not even light, can escape its grip. But that’s just one of the ways in which black holes bend our conception of reality.

Light waves from stars behind a black hole are bent by its gravitational field, which produces the aura you see around the circular edge of the event horizon.

Oh, the event horizon … This is important. That marks the edge of the region where anything that falls in can’t get out. But if you were heading toward the event horizon, you wouldn’t necessarily know when you crossed it – at least at first. You could keep falling toward the center of a black hole for hours before bad stuff starts happening.

Eventually, though, the gravitational field would become so strong that if you were falling feet first, your feet would be pulled in faster than your head. Your whole body, and all the atoms in it, would be stretched out like a noodle. Stephen Hawking is credited with coming up with the technical term for this effect: spaghettification.

Once an object falls past the event horizon, it’s gone. But for physicists like Hawking, that’s a big problem. In science class, you’ve probably heard it said that energy can neither be created nor destroyed – it can only be transferred or changed in form. Theoretical physicists say the same thing about information: It can neither be created nor destroyed.

So what happens to the information about things that fall in a black hole? Some physicists say that the information is somehow encoded on the surface of the event horizon, perhaps as tiny fluctuations in a black hole’s gravitational field.

It’s similar to the way the information for a 3-D object can be encoded on a 2-D hologram – like the shiny square that’s on the back of a credit card. Physicists call this idea the holographic principle. Some even suggest that at its most basic level, the universe we live in just might be an encoded two-dimensional surface that we decode into our perception of three dimensions.

If that’s the case, it’s not hard to imagine that everything in our reality – including ourselves – can be translated into the code of a deeper reality. And if our descendants ever figure out that code, maybe millions of years from now, could our shades be re-created from the fluctuations we left behind? What is real?

I’m going to stop right here, at the edge of the event horizon. I’ll leave it to the actors of “The Primrose Protocol” to plunge ahead, into the void.

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Readings hint at black hole eating neutron star

Scientists work in the LIGO Hanford control room. (Caltech / MIT / LIGO Lab Photo / C. Gray)

The science teams for the Laser Interferometer Gravitational-Wave Observatory, or LIGO, and Europe’s Virgo detector today laid out the details of their recent detections, including a crash between neutron stars, three black hole mergers and what may be the first observed collision of a neutron star and a black hole.

Astronomers and their fans have been talking about the detections for days, thanks to the fact that LIGO and Virgo are quickly sharing the raw results from their current observing run. But today’s statements provided the most authoritative views from researchers running the two gravitational-wave detectors.

The April 26 detection of a cosmic collision known as S190426c is the most intriguing event. The subtle signal of a far-off disturbance in the gravitational force was picked up by LIGO’s twin detectors at Hanford in Eastern Washington and at Livingston in Louisiana. The Virgo detector in Italy also detected the signal.

The signal is consistent with what might be expected if a black hole were to swallow a neutron star, roughly 1.2 billion light-years from Earth. Such an event has never been observed before.

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Scientists unveil first image of a black hole

Black hole image
This image from the Event Horizon Telescope shows the supermassive black hole in the elliptical galaxy M87, surrounded by superheated material. (EHT Collaboration)

WASHINGTON, D.C. — Scientists today shared the first picture to show the immediate surroundings of a galaxy’s supermassive black hole, captured by a network of radio telescopes that adds up to what could be considered the world’s widest observatory.

A project called the Event Horizon Telescope delivered a fuzzy view of the dark monster at the center of an elliptical galaxy known as M87. The edge of the black hole’s dark circle, known as the event horizon, was surrounded by the bright glare of superheated material falling into the black hole.

“This is a remarkable achievement. … It’s almost humbling in a certain way,” EHT project director Shep Doeleman, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said during a news briefing here at the National Press Club.

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