Off the Pacific coast of Costa Rica sits a deep-sea chimera of an ecosystem. Jacó Scar is a methane seep, where the gas escapes from sediment into the seawater, but the seep isn’t cold like the others found before it. Instead, geochemical activity gives the Scar lukewarm water that enables organisms from both traditionally colder seeps and scalding hot hydrothermal vents to call it home.
One resident of the Scar is a newly identified species of small, purplish fish called an eelpout, described for the first time on January 19 in Zootaxa. This fish is the first vertebrate species found at the Scar and could help scientists understand how the unique ecosystem developed. Jacó Scar was discovered during exploration of a known field of methane seeps off the Costa Rican coast and named for the nearby town of Jacó. It is “a really diverse place” with many different organisms living in various microhabitats, says Lisa Levin, a marine ecologist at Scripps Institution of Oceanography in La Jolla, Calif.
Levin was on one of the first expeditions to the Scar but wasn’t involved in the new study. She recalls the team finding and collecting one of the fish during this early excursion, but the researchers didn’t recognize it as a new species.
Several more specimens were snagged during later submersible dives. Charlotte Seid, an invertebrate biologist at Scripps who is working on a checklist of organisms found at the Costa Rican seeps, brought the fishy finds to ichthyologist Ben Frable, also of Scripps, for formal identification.
Frable says he knew the fish was an eelpout. They look exactly as one would expect based on their name: like frowning eels, though they aren’t true eels. But he was having trouble determining what type. Eelpouts are a diverse family of fish comprised of nearly 300 species that can be found all over the world at various ocean depths.
Because the physical differences between species can be subtle, they are “kind of a tricky group” to identify, Frable says. “I just was not really getting anywhere.” So the team turned to eelpout expert Peter Rask Møller of the Natural History Museum of Denmark in Copenhagen, sending him X-rays, pictures and eventually one of the fish specimens.
Møller narrowed the enigmatic eelpout to the genus Pyrolycus, meaning “fire wolf.” Turns out, the tool, called a dichotomous key, that Frable had been using to identify the specimens was outdated, made before Pyrolycus was described in 2002. “I did not know that genus existed,” Frable says.
Because the other two known Pyrolycus species live far away in the western Pacific and have different physical features, the team dubbed the mystery fish P. jaco — a new species.
The first eelpouts most likely evolved in cold waters, Frable says, but many have since made their home in the scalding waters of hydrothermal vents. Of the 24 known fish species that live only at hydrothermal vents, “13 of them are eelpouts,” Frable says. The new finding raises questions about how the known Pyrolycus species came to live so far apart. It may have to do with the fact that methane seeps are more common than previously thought on the ocean floor, and if some are lukewarm like Jacó Scar, the new species could have used them as refuges while moving east.
And by comparing P. jaco to its vent-living relatives, researchers may be able to figure out how it adapted to live in the tepid waters of the Scar — which may provide clues to how other species living there did too.
The eelpout is part of a medley of other species that form Jacó Scar’s composite ecosystem, along with, for example, clams typically found at cold seeps and bacteria found at hydrothermal vents. Jacó Scar is a “mixing bowl” of species found in other parts of the world, Seid says. Figuring out how this eclectic bunch interacts “is part of the fun.”
Editor’s note: On April 10, the Event Horizon Telescope collaboration released a picture of the supermassive black hole at the center of galaxy M87. Read the full story here.
We’re about to see the first close-up of a black hole.
The Event Horizon Telescope, a network of eight radio observatories spanning the globe, has set its sights on a pair of behemoths: Sagittarius A*, the supermassive black hole at the Milky Way’s center, and an even more massive black hole 53.5 million light-years away in galaxy M87 (SN Online: 4/5/17). In April 2017, the observatories teamed up to observe the black holes’ event horizons, the boundary beyond which gravity is so extreme that even light can’t escape (SN: 5/31/14, p. 16). After almost two years of rendering the data, scientists are gearing up to release the first images in April.
Here’s what scientists hope those images can tell us.
What does a black hole really look like? Black holes live up to their names: The great gravitational beasts emit no light in any part of the electromagnetic spectrum, so they themselves don’t look like much.
But astronomers know the objects are there because of a black hole’s entourage. As a black hole’s gravity pulls in gas and dust, matter settles into an orbiting disk, with atoms jostling one another at extreme speeds. All that activity heats the matter white-hot, so it emits X-rays and other high-energy radiation. The most voraciously feeding black holes in the universe have disks that outshine all the stars in their galaxies (SN Online: 3/16/18). The EHT’s image of the Milky Way’s Sagittarius A, also called SgrA, is expected to capture the black hole’s shadow on its accompanying disk of bright material. Computer simulations and the laws of gravitational physics give astronomers a pretty good idea of what to expect. Because of the intense gravity near a black hole, the disk’s light will be warped around the event horizon in a ring, so even the material behind the black hole will be visible. And the image will probably look asymmetrical: Gravity will bend light from the inner part of the disk toward Earth more strongly than the outer part, making one side appear brighter in a lopsided ring.
Does general relativity hold up close to a black hole? The exact shape of the ring may help break one of the most frustrating stalemates in theoretical physics.
The twin pillars of physics are Einstein’s theory of general relativity, which governs massive and gravitationally rich things like black holes, and quantum mechanics, which governs the weird world of subatomic particles. Each works precisely in its own domain. But they can’t work together.
“General relativity as it is and quantum mechanics as it is are incompatible with each other,” says physicist Lia Medeiros of the University of Arizona in Tucson. “Rock, hard place. Something has to give.” If general relativity buckles at a black hole’s boundary, it may point the way forward for theorists.
Since black holes are the most extreme gravitational environments in the universe, they’re the best environment to crash test theories of gravity. It’s like throwing theories at a wall and seeing whether — or how — they break. If general relativity does hold up, scientists expect that the black hole will have a particular shadow and thus ring shape; if Einstein’s theory of gravity breaks down, a different shadow.
Medeiros and her colleagues ran computer simulations of 12,000 different black hole shadows that could differ from Einstein’s predictions. “If it’s anything different, [alternative theories of gravity] just got a Christmas present,” says Medeiros, who presented the simulation results in January in Seattle at the American Astronomical Society meeting. Even slight deviations from general relativity could create different enough shadows for EHT to probe, allowing astronomers to quantify how different what they see is from what they expect. Do stellar corpses called pulsars surround the Milky Way’s black hole? Another way to test general relativity around black holes is to watch how stars careen around them. As light flees the extreme gravity in a black hole’s vicinity, its waves get stretched out, making the light appear redder. This process, called gravitational redshift, is predicted by general relativity and was observed near SgrA* last year (SN: 8/18/18, p. 12). So far, so good for Einstein.
An even better way to do the same test would be with a pulsar, a rapidly spinning stellar corpse that sweeps the sky with a beam of radiation in a regular cadence that makes it appear to pulse (SN: 3/17/18, p. 4). Gravitational redshift would mess up the pulsars’ metronomic pacing, potentially giving a far more precise test of general relativity.
“The dream for most people who are trying to do SgrA* science, in general, is to try to find a pulsar or pulsars orbiting” the black hole, says astronomer Scott Ransom of the National Radio Astronomy Observatory in Charlottesville, Va. “There are a lot of quite interesting and quite deep tests of [general relativity] that pulsars can provide, that EHT [alone] won’t.”
Despite careful searches, no pulsars have been found near enough to SgrA* yet, partly because gas and dust in the galactic center scatters their beams and makes them difficult to spot. But EHT is taking the best look yet at that center in radio wavelengths, so Ransom and colleagues hope it might be able to spot some.
“It’s a fishing expedition, and the chances of catching a whopper are really small,” Ransom says. “But if we do, it’s totally worth it.” How do some black holes make jets? Some black holes are ravenous gluttons, pulling in massive amounts of gas and dust, while others are picky eaters. No one knows why. SgrA* seems to be one of the fussy ones, with a surprisingly dim accretion disk despite its 4 million solar mass heft. EHT’s other target, the black hole in galaxy M87, is a voracious eater, weighing in at between about 3.5 billion and 7.22 billion solar masses. And it doesn’t just amass a bright accretion disk. It also launches a bright, fast jet of charged subatomic particles that stretches for about 5,000 light-years.
“It’s a little bit counterintuitive to think a black hole spills out something,” says astrophysicist Thomas Krichbaum of the Max Planck Institute for Radio Astronomy in Bonn, Germany. “Usually people think it only swallows something.”
Many other black holes produce jets that are longer and wider than entire galaxies and can extend billions of light-years from the black hole. “The natural question arises: What is so powerful to launch these jets to such large distances?” Krichbaum says. “Now with the EHT, we can for the first time trace what is happening.”
EHT’s measurements of M87’s black hole will help estimate the strength of its magnetic field, which astronomers think is related to the jet-launching mechanism. And measurements of the jet’s properties when it’s close to the black hole will help determine where the jet originates — in the innermost part of the accretion disk, farther out in the disk or from the black hole itself. Those observations might also reveal whether the jet is launched by something about the black hole itself or by the fast-flowing material in the accretion disk.
Since jets can carry material out of the galactic center and into the regions between galaxies, they can influence how galaxies grow and evolve, and even where stars and planets form (SN: 7/21/18, p. 16).
“It is important to understanding the evolution of galaxies, from the early formation of black holes to the formation of stars and later to the formation of life,” Krichbaum says. “This is a big, big story. We are just contributing with our studies of black hole jets a little bit to the bigger puzzle.”
Editor’s note: This story was updated April 1, 2019, to correct the mass of M87’s black hole; the entire galaxy’s mass is 2.4 trillion solar masses, but the black hole itself weighs in at several billion solar masses. In addition, the black hole simulation is an example of one that uphold’s Einstein’s theory of general relativity, not one that deviates from it.
