Connect with us

Space

A runaway black hole has been spotted fleeing a distant galaxy

Published

on

030723_lg_blackhole_feat.jpg


Advertisement

A streak of light stretching away from a remote galaxy might be the first sure sign of a gargantuan black hole on the run, a new study reports. The putative black hole, fleeing its host galaxy, appears to be leaving a trail of newborn stars and shocked gas in its wake. If confirmed, the intergalactic escape could help astronomers learn more about what happens to black holes when galaxies collide.

“It’s a very cool, serendipitous discovery,” says astronomer Charlotte Angus of the University of Copenhagen, who was not involved in the new work. “The possibility that this might be due to a supermassive black hole that’s been ejected from its galaxy is very exciting. These events have been predicted by theory, but up until now, there’s been little evidence for them.”

Advertisement

While looking for colliding dwarf galaxies with the Hubble Space Telescope, astronomer Pieter van Dokkum and colleagues spotted something peculiar: a long, straight line that seemed to extend away from a distant galaxy, growing narrower and brighter as it went (SN: 5/18/22).

Advertisement

“Whatever it is, we haven’t seen it before,” says van Dokkum, of Yale University. “Most astronomical objects are shaped like a spiral or a blob. There are not many objects that are just a line in the sky.” When astronomers do see lines, they’re usually from something moving, like a satellite crossing the telescope’s field of view (SN: 3/3/23).

To figure out what it was, van Dokkum and colleagues took follow-up observations with the Keck Observatory in Hawaii. Those observations showed that the streak was associated with a galaxy whose light took about 8 billion years — more than half the age of the universe — to get to Earth, the team reports in a paper submitted February 9 to arXiv.org. The distance measurement let the team calculate the length of the line: roughly 200,000 light-years.

Advertisement

That certainly ruled out a satellite.

“We considered a lot of explanations, and the one that fit the best is what we’re witnessing is a massive object, like a black hole, moving very rapidly away from the galaxy,” van Dokkum says.

Advertisement
An image from the Hubble Space Telescope that shows a runaway black hole as a straight white line.
The runaway black hole showed up as a straight line in a Hubble image (shown). The origin galaxy is at the top right of the streak. The galaxy is so far away that the line stretches for 200,000 light-years.P. van Dokkum et al/arXiv.org 2023

Black holes on their own are invisible. But “if a black hole leaves a galaxy, it doesn’t leave by itself,” van Dokkum says. Some of the stars and gas that were gravitationally bound to the black hole leave with it. That gas will emit strong radiation that telescopes can detect. The black hole’s path through the gas and dust in the galaxy’s outer regions can compress some of that gas into new stars, too, which would also be visible (SN: 7/12/18).

Another possibility is that the line is a jet of radiation launched by the galaxy’s central supermassive black hole. But that scenario would probably lead to a beam that is narrow when it is close to the galaxy and broadens as it gets farther away. This streak does the opposite.

If it’s a black hole, it could have been ejected from the galaxy’s center by interacting with one or two other black holes nearby. Almost every galaxy has a supermassive black hole at its center. When galaxies merge, their central black holes also eventually merge (SN: 3/5/21). If the conditions are right, that merger can give the resulting black hole a “kick,” sending it flying away at high speed (SN: 4/25/22).

Advertisement

Alternatively, the black hole could have been spat out of a smashup among three galaxies. When a third galaxy joins an ongoing merger, three supermassive black holes jockey for position. One black hole can be tossed out of the galactic smashup, while the other two take off more slowly in the other direction.

That’s what van Dokkum thinks happened in this case. There are signs of a shorter, dimmer streak heading in the opposite direction from the bright, straight line.

Advertisement

More observations of this system, perhaps with the James Webb Space Telescope, are needed to confirm that it really is an ejected supermassive black hole, Angus says. More theoretical calculations of what a runaway supermassive black hole should look like would help too.

The finding motivates Angus to search through archived data for more potential black hole streaks. “I wonder if there are more of these features out there, sitting in someone’s data that might have just been missed,” she says.

Advertisement

Van Dokkum does too. “Now that we know what to look for, these very thin streaks, it makes sense to go back to Hubble data. We have 25 years of Hubble images that have not been searched with this purpose,” he says. “If there are more to be found, I think we can do it.”



Source link

Advertisement

Advertisement

Space

TRAPPIST-1’s biggest planet doesn’t have much, or any, atmosphere

Published

on

By

032423_SP_trappist_feat.jpg



A rocky planet that circles a small star nearly 40 light-years from Earth is hot and has little or no atmosphere, a new study suggests. The finding raises questions about the possibility of atmospheres on the other orbs in the planetary system.

Advertisement

At the center of the system is the red dwarf star dubbed TRAPPIST-1; it hosts seven known planets with masses ranging from 0.3 to 1.4 times Earth’s, a few of which could hold liquid water (SN: 2/22/17; 3/19/18). The largest, TRAPPIST-1b, is the closest to its parent star and receives about four times the radiation Earth receives from the sun, says Thomas Greene, an astrobiologist at NASA’s Ames Research Center at Moffett Field, Calif.

Like all other planets in the system, TRAPPIST-1b is tidally locked, meaning that one side of the planet always faces the star, and one side looks away. Calculations suggest that if the stellar energy falling on TRAPPIST-1b were distributed around the planet — by an atmosphere, for example — and then reradiated equally in all directions, the planet’s surface temperature would be around 120° Celsius.

But the dayside temperature of the planet is actually around 230° C, Greene and colleagues report online March 27 in Nature. That, in turn, suggests that there’s little or no atmosphere to carry heat from the perpetually sunlit side of the planet to the dark side, the team argues.

Advertisement

To take TRAPPIST-1b’s temperature, Greene and his colleagues used the James Webb Space Telescope to observe the planet in a narrow band of infrared wavelengths five times in 2022. Because the observations were made just before and after the planet dodged behind its parent star, astronomers could see the fully lit face of the planet, Greene says.

The team’s results are “the first ‘deep dive’ look at this planet,” says Knicole Colon, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md, who was not involved with the study. “With every observation, we expect to learn something new,” she adds.

Advertisement

Astronomers have long suggested that planets around red dwarf stars might not be able to hold onto their atmospheres, largely because such stars’ frequent and high-energy flares would blast away any gaseous shroud they might have during their early years (SN: 12/20/22). Yet there are some scenarios in which such flares could heat up a planet’s surface and drive volcanism that, in turn, yields gases that could help form a new atmosphere.

“To be totally sure that this planet has no atmosphere, we need many more measurements,” says Michaël Gillon, an astrophysicist at the University of Liège in Belgium who was not part of the new study. It’s possible that when observed at a wider variety of wavelengths and from other angles, the planet could show signs of a gaseous shroud and thus possibly hints of volcanism.

Advertisement

Either way, says Laura Kriedberg, an astronomer at the Max Planck Institute for Astronomy in Heidelberg, Germany, who also did not participate in the study, the new result “definitely motivates detailed study of the cooler planets in the system, to see if the same is true of them.”



Source link

Advertisement

Advertisement
Continue Reading

Space

A neutron star collision may have emitted a fast radio burst

Published

on

By

032423_LG_neutron-star_feat.jpg



A neutron star pileup may have emitted two different kinds of cosmic signals: ripples in spacetime known as gravitational waves and a brief blip of energy called a fast radio burst.

Advertisement

One of the three detectors that make up the gravitational wave observatory LIGO picked up a signal from a cosmic collision on April 25, 2019. About 2.5 hours later, a fast radio burst detector picked up a signal from the same region of sky, researchers report March 27 in Nature Astronomy.

If strengthened by further observations, the finding could bolster the theory that mysterious fast radio bursts have multiple origins — and neutron star mergers are one of them.

“We’re 99.5 percent sure” the two signals came from the same event, says astrophysicist Alexandra Moroianu, who spotted the merger and its aftermath while at the University of Western Australia in Perth. “We want to be 99.999 percent sure.”

Advertisement

Unfortunately, LIGO’s two other detectors didn’t catch the signal, so it’s impossible to precisely triangulate its location. “Even though it’s not a concrete, bang-on observation for something that’s been theorized for a decade, it’s the first evidence we’ve got,” Moroianu says. “If this is true … it’s going to be a big boom in fast radio burst science.”

Mysterious radio bursts

Astronomers have spotted more than 600 fast radio bursts, or FRBs, since 2007. Despite their frequency, the causes remain a mystery. One leading candidate is a highly magnetized neutron star called a magnetar, which could be left behind after a massive star explodes (SN: 6/4/20). But some FRBs appear to repeat, while others are apparent one-off events, suggesting that there’s more than one way to produce them (SN: 2/7/20).

Advertisement

Theorists have wondered if a collision between two neutron stars could spark a singular FRB, before the wreckage from the collision produces a black hole. Such a smashup should emit gravitational waves, too (SN: 10/16/17).

Moroianu and colleagues searched archived data from LIGO and the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, a fast radio burst detector in British Columbia, to see if any of their signals lined up. The team found one candidate pairing: GW190425 and FRB20190425A.

Advertisement

Even though the gravitational wave was picked up only by the LIGO detector in Livingston, La., the team spotted other suggestive signs that the signals were related. The FRB and the gravitational waves came from the same distance, about 370 million light-years from Earth. The gravitational waves were from the only neutron star merger LIGO spotted in that observing run, and the FRB was particularly bright. There may even have been a burst of gamma rays at the same time, according to satellite data — another aftereffect of a neutron star merger.

Advertisement

“Everything points at this being a very interesting combination of signals,” Moroianu says. She says it’s like watching a crime drama on TV: “You have so much evidence that anyone watching the TV show would be like, ‘Oh, I think he did it.’ But it’s not enough to convince the court.”

Neutron star secrets

Despite the uncertainty, the finding has exciting implications, says astrophysicist Alessandra Corsi of Texas Tech University in Lubbock. One is the possibility that two neutron stars could merge into a single, extra-massive neutron star without immediately collapsing into a black hole. “There’s this fuzzy dividing line between what’s a neutron star and what’s a black hole,” says Corsi, who was not involved in the new work.

Advertisement

In 2013, astrophysicist Bing Zhang of the University of Nevada, Las Vegas suggested that a neutron star smashup could create an extra-massive neutron star that wobbles on the edge of stability for a few hours before collapsing into a black hole. In that case, the resulting FRB would be delayed — just like in the 2019 case.

The most massive neutron star yet observed is about 2.35 times the mass of the sun, but theorists think they could grow to be around three times the mass of the sun without collapsing (SN: 7/22/22). The neutron star that could have resulted from the collision in 2019 would have been 3.4 solar masses, Moroianu and colleagues calculate.

Advertisement

“Something like this, especially if it’s confirmed with more observations, it would definitely tell us something about how neutron matter behaves,” Corsi says. “The nice thing about this is we have hopes of testing this in the future.”

The next LIGO run is expected to start in May. Corsi is optimistic that more coincidences between gravitational waves and FRBs will show up, now that researchers know to look for them. “There should be a bright future ahead of us,” she says.

Advertisement



Source link

Advertisement
Continue Reading

Space

Scientists Explain Why Jupiter’s and Saturn’s Icy Moons Have Extreme Radar Properties | Sci.News

Published

on

By

image_11772-Europa.jpg


Advertisement
The radar properties of icy satellites of Jupiter and Saturn commonly differ by more than an order of magnitude from those of rocky planets because of the lower absorptivity of water ice than that of rock. However, the specific mechanisms behind these differences are not confidently known yet.
An artist’s impression of the surface of Jupiter’s icy moon Europa. Image credit: NASA / JPL-Caltech / SwRI.

An artist’s impression of the surface of Jupiter’s icy moon Europa. Image credit: NASA / JPL-Caltech / SwRI.

Advertisement

“Six different models have been published in an attempt to explain the radar signatures of the icy moons that orbit Jupiter and Saturn,” said Southwest Research Institute senior research scientist Dr. Jason Hofgartner.

“The way these objects scatter radar is drastically different than that of the rocky worlds, such as Mars and Earth, as well as smaller bodies such as asteroids and comets.”

Advertisement

The Jovian and Saturnian moons are also extremely bright, even in areas where they should be darker.

“When we look up at Earth’s moon it looks like a circular disk, even though we know it’s a sphere,” Dr. Hofgartner said.

Advertisement

“Planets and other moons similarly look like disks through telescopes.”

“While making radar observations, the center of the disk is very bright and the edges much darker.”

Advertisement

“The change from center to edge is very different for these icy satellites than for rocky worlds.”

Dr. Hofgartner and his colleague, Dr. Kevin Hand from NASA’s Jet Propulsion Laboratory, argue that the extraordinary radar properties of these satellites, such as their reflectiveness and polarization (the orientation of light waves as they propagate through space) is very likely to be explained by the coherent backscatter opposition effect (CBOE).

Advertisement

“When you’re at opposition, the Sun is positioned directly behind you on the line between you and an object, the surface appears much brighter than it would otherwise,” Dr. Hofgartner said.

“This is known as the opposition effect. In the case of radar, a transmitter stands in for the Sun and a receiver for your eyes.”

Advertisement

“An icy surface has an even stronger opposition effect than normal.”

“For every scattering path of light bouncing through the ice, at opposition there is a path in the exact opposite direction.”

Advertisement

“Because the two paths have precisely the same length, they combine coherently, resulting in further brightening.”

In the 1990s, studies were published stating that the CBOE was one explanation for the anomalous radar signatures of icy satellites, but other explanations could explain the data equally well.

Advertisement

Dr. Hofgartner and Dr. Hand improved the polarization description of the CBOE model and also showed that their modified CBOE model is the only published model that can explain all of the icy satellite radar properties.

“I think that tells us that the surfaces of these objects and their subsurfaces down to many meters are very tortured,” Dr. Hofgartner said.

Advertisement

“They’re not very uniform. Icy rocks dominate the landscape, perhaps looking somewhat like the chaotic mess after a landslide.”

“That would explain why the light is bouncing in so many different directions, giving us these unusual polarization signatures.”

Advertisement

A paper describing the findings was published in the journal Nature Astronomy.

_____

Advertisement

J.D. Hofgartner & K.P. Hand. A continuum of icy satellites’ radar properties explained by the coherent backscatter effect. Nat Astron, published online March 23, 2023; doi: 10.1038/s41550-023-01920-2



Source link

Advertisement

Advertisement
Continue Reading

Trending