Astronomers Will Soon Have the First-Ever Picture of a Black Hole

The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A*, located in the middle, as captured in x-ray and infrared in this 2013 NASA photo.
The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A*, located in the middle, as captured in x-ray and infrared in this 2013 NASA photo.
NASA/UMass/D.Wang et al., IR: NASA/STScI

It may not be the closest black hole to Earth, but it’s certainly the closest one that astronomers have labeled as "supermassive." Known as Sagittarius A* (pronounced “Sagittarius A-star”), the mysterious object, first detected in the 1970s, weighs as much as 4 million Suns. Formed by the collapse of large stars, most black holes aren't nearly that size.

Sagittarius A* sits at the very heart of the Milky Way galaxy, some 25,000 light-years from our solar system—but until now, we haven’t known much about it. Soon, however, thanks to a globe-spanning array of radio telescopes known as the Event Horizon Telescope, astronomers will have their closest ever look at this enigmatic object.

The Event Horizon Telescope, or EHT, is named for the infamous “point of no return” that marks the outer boundary of a black hole. (The gravity of a black hole is so strong that nothing can escape it, not even light—thus the name.) It incorporates huge, dish-shaped telescopes at six different sites on four continents, including Antarctica and Hawaii. The array recently completed its most ambitious observation so far, collecting data of Sagittarius A* over a 10-day period in mid-April.

“We’ve never had data of the quality that we’ve just taken,” Dan Marrone, an experimental astrophysicist at the University of Arizona, tells Mental Floss. When the data is eventually processed—sometime this fall at the earliest—astronomers will have their clearest picture yet of a black hole.

A VIEW OF THE EDGE

What that image will actually look like, however, is still very much up in the air. We know that black holes are typically surrounded by accretion disks—rings of dust and gas that swirl around the black hole, getting ever-hotter as the material approaches the black hole’s event horizon. The in-falling matter gets so hot that it emits radio waves and other radiation (which is how objects like Sagittarius A* were first detected). Accretion disks can also produce jets—streams of high-energy particles that get blasted out from the black hole at nearly the speed of light. And we know that the system’s intense gravity bends starlight as it passes near the black hole. “We might see a crescent, brightened on one side—or a bipolar, jet-like structure,” Marrone says. “We honestly don’t know.”

Standard optical telescopes—even those high above the Earth’s atmosphere, like Hubble—can tell us very little about objects like Sagittarius A* because there’s too much gas and dust between us and the galactic center for optical wavelengths to penetrate; it’s like trying to peer across San Francisco Bay on the foggiest day of the year.

But radio telescopes, taking advantage of the longer wavelengths of radio waves, can see through the murk. The best bet, astronomers have found, is to use telescopes sensitive to wavelengths of about 1 centimeter—longer than wavelengths of infrared light, but shorter than the waves that your car radio picks up.

Multiple radio telescopes, in different locations, can be made to work together even better, simulating a much larger instrument. This technique is known as VLBI, for Very Long Baseline Interferometry. The Atacama Large Millimeter-submillimeter Array, comprising 66 radio dishes in northern Chile, was recently added to the EHT array, greatly boosting the overall sensitivity; the South Pole Telescope was also added to the array in April. The project now involves 30 institutions in 12 countries.

“The Event Horizon Telescope is going to be zooming in, to right where the inner edge of the accretion disk is falling in to the black hole—right at the boundary between where the disk material ends and the black hole starts,” radio astronomer Joseph Lazio of NASA’s Jet Propulsion Laboratory tells Mental Floss.

A BLACK HOLE WITHOUT MUCH OF AN APPETITE

Of course, we can never see past the event horizon—whatever’s on the other side remains forever beyond our reach. But with the resolving power of the EHT, astronomers will have their closest look yet at the region immediately outside it.

The EHT’s resolving power will be so crucial because, despite Sagittarius A*’s heft, it’s not very large in terms of size. Its event horizon is believed to span just about 15 million miles—less than 20 times the diameter of the Sun.

And in spite of the public perception of black holes as “cosmic vacuum cleaners” that suck up everything in sight, Sagittarius A* is actually not much of an eater. “It’s on a starvation diet,” Marrone jokes. “We don’t know of another black hole that’s eating so slowly, relative to its weight.”

Another target for the EHT will be the black hole in the center of a galaxy known as M87. This ginormous black hole is 1000 times farther away than Sagittarius A*, but it’s also 1000 times more massive; it’s so big that its gravity anchors an entire cluster of galaxies, known as the Virgo Cluster. And it has enormous jets shooting out of its accretion disk—something that astronomers are anxious to get a closer look at.

Beyond simply imaging these giant black holes, the EHT may shed some light on the complex relationship between supermassive black holes and the galaxies that harbor them. Surveys using X-ray telescopes suggest that these overweight black holes are common; they’re believed to lurk in the hearts of most galaxies. But did the galaxies evolve first, and then the black holes—or was it the other way around?

WHAT CAME FIRST, THE BLACK HOLE OR THE GALAXY?

“There’s a very strong correlation between the properties of these supermassive black holes and the properties of their host galaxies,” David Spergel, a Princeton astrophysicist and director of the Center for Computational Astrophysics, tells Mental Floss. “So they’re linked together—but this is a chicken-and-egg question that we don’t know the answer to.”

Another motivation for studying black holes is to determine whether Einstein’s theory of gravity, known as general relativity, correctly predicts the observed physics. The theory, which turned 100 last year, has so far passed every test thrown at it—but it has yet to be tested in the exotic environment adjacent to a black hole event horizon, with its ultra-strong gravitational field. “You’re probing a new regime—and whenever you’re in a new regime, you could be in for a surprise,” Spergel says.

The astronomers working on the EHT won’t see the fruits of their labors right away: Each of the facilities in the array recorded about 500 terabytes of data during this spring’s observing run—far too much to be conveniently sent over the internet. So the data is being sent the old-fashioned way, by shipping bulky drives via FedEx to the EHT’s two processing centers, located in Westford, Massachusetts and in Bonn, Germany. (That doesn’t include the disks from the South Pole Telescope; they’ll be shipped later in the year, when planes can access the site after the Antarctic winter.) Then the data needs to be processed, which will take some six to eight months.

Asked if he was feeling tense, Marrone replied that “anticipation” was a better word; after all the testing he and his colleagues have done, he’s pretty confident that the EHT has delivered the goods. “I’d like to know what we’ve got in those data,” he said. “But it’s going to be a long wait.”

Bombshell, Victoria’s Secret’s Bestselling Fragrance, Also Happens to Repel Mosquitoes

Dids, Pexels
Dids, Pexels

People love Bombshell, the best-selling fragrance at Victoria’s Secret, for its summery blend of fruity and floral notes. Not everyone is a huge fan, though: As Quartz reports, the perfume is surprisingly good at warding off mosquitoes. In fact, it’s almost as effective as DEET insect repellent, according to the results of a 2014 experiment by researchers at New Mexico State University.

Researchers took 10 products that are commercially available and tested their ability to repel two different species of mosquitoes: the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus), both of which are known to transmit diseases like dengue fever, chikungunya, and yellow fever. In doing so, volunteers subjected their own flesh to the test by placing their hands on either side of a Y-shaped tube containing the blood-sucking critters. One hand was covered in a synthetic rubber glove, while the other hand was sprayed with one of the products but otherwise left bare. Researchers recorded which tunnel the mosquitoes flew to, and how long they avoided the other end.

Three of the products contained DEET, while four products didn’t. In addition, there were two fragrances (including Bombshell) and one vitamin B1 skin patch. The DEET products were the most effective, but Bombshell proved to be nearly as good, keeping mosquitoes at bay for roughly two hours.

“There was some previous literature that said fruity, floral scents attracted mosquitoes, and to not wear those,” Stacy Rodriquez, one of the study’s authors, said in a statement. “It was interesting to see that the mosquitoes weren’t actually attracted to the person that was wearing the Victoria’s Secret perfume—they were repelled by it.”

This isn’t the first time a perfume has had an unintended effect on the natural world. It turns out that tigers are obsessed with Calvin Klein’s Obsession for Men cologne, partly because it contains a synthetic version of civetone, a pheromone that's secreted by glands located near a civet’s anus. This substance was once used to create musky fragrances, but nowadays the scent is mostly reproduced in a lab. Still, the fake stuff must be pretty convincing, because big cats go crazy when they catch a whiff of it.

[h/t Quartz]

Mystery Solved: Scientists Have Figured Out Why Some Squirrels Are Black

Rena-Marie/iStock via Getty Images
Rena-Marie/iStock via Getty Images

It can be something of a surprise to see an animal sporting a fresh coat of paint. Blue lobsters occasionally surface after being caught in traps. A pink dolphin was spotted in Louisiana in 2007 (and several times since). In the Chinese province of Shaanxi, a cute brown and white panda greets zoo visitors.

Another anomalous animal has joined their ranks. Black squirrels have been spotted in both the United States and the UK, and now scientists believe they know why.

Like many animals with unusual color schemes, black squirrels are the result of a genetic detour. Researchers at Anglia Ruskin University, Cambridge University, and the Virginia Museum of Natural History collaborated on a project that tested squirrel DNA. Their findings, which were published in BMC Evolutionary Biology, demonstrated that the black squirrel is the product of interspecies breeding between the common gray squirrel and the fox squirrel. The black squirrel is actually a gray squirrel with a faulty pigment gene carried over from the fox squirrel that turns their fur a darker shade. (Some fox squirrels, which are usually reddish-brown, are also black.)

A black squirrel is pictured
sanches12/iStock via Getty Images

Scientists theorize a black fox squirrel may have joined in on a mating chase involving gray squirrels and got busy with a female. The black fur may offer benefits in colder regions, with squirrels able to absorb and retain more heat, giving them a slight evolutionary edge.

In North America, black squirrels are uncommon, with one estimate putting them at a rate of one in every 10,000 squirrels. In 1961, students at Kent State University in Ohio released 10 black squirrels that had been captured by Canadian wildlife authorities. The squirrels now populate the campus and have become the school’s unofficial mascot. Their coloring might help them hide from predators, which might come in handy at Kent State: The campus is also home to hawks.

[h/t The Guardian]

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