Astronomy

Fragmenting planets sweeping extremely close to their stars might be the cause of mysterious cosmic blasts of radio waves.

Milliseconds-long fast radio bursts, or FRBs, erupt from distant cosmic locales. Some of these bursts blast only once and others repeat. A new computer calculation suggests the repetitive kind could be due to a planet interacting with its magnetic host star, researchers report in the March 20 Astrophysical Journal.

FRBs are relative newcomers to astronomical research. Ever since the first was discovered in 2007, researchers have added hundreds to the tally. Scientists have theorized dozens of ways the two different types of FRBs can occur, and nearly all theories include compact, magnetic stellar remnants known as neutron stars. Some ideas include powerful radio flares from magnetars, the most magnetic neutron stars imaginable (SN: 6/4/20). Others suggest a fast-spinning neutron star, or even asteroids interacting with magnetars (SN: 2/23/22).

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“How fast radio bursts are produced is still up for debate,” says astronomer Yong-Feng Huang of Nanjing University in China.

Huang and his colleagues considered a new way to make the repeating flares: interactions between a neutron star and an orbiting planet (SN: 3/5/94). Such planets can get exceedingly close to these stars, so the team calculated what might happen to a planet in a highly elliptical orbit around a neutron star. When the planet swings very close to its star, the star’s gravity pulls more on the planet than when the planet is at its farthest orbital point, elongating and distorting it. This “tidal pull,” Huang says, will rip some small clumps off the planet. Each clump in the team’s calculation is just a few kilometers wide and maybe one-millionth the mass of the planet, he adds.

Then the fireworks start. Neutron stars spew a wind of radiation and particles, much like our own sun but more extreme. When one of these clumps passes through that stellar wind, the interaction “can produce really strong radio emissions,” Huang says. If that happens when the clump appears to pass in front of the star from Earth’s perspective, we might see it as a fast radio burst. Each burst in a repeating FRB signal could be caused by one of these clumps interacting with the neutron star’s wind during each close planet pass, he says. After that interaction, what remains of the clump drifts in orbit around the star, but away from Earth’s perspective, so we never see it again.

Comparing the calculated bursts to two known repeaters — the first ever discovered, which repeats roughly every 160 days, and a more recent discovery that repeats every 16 days, the team found the fragmenting planet scenario could explain how often the bursts happened and how bright they were (SN: 3/2/16).

The star’s strong gravitational “tidal” pull on the planet during each close pass might change the planet’s orbit over time, says astrophysicist Wenbin Lu of Princeton University, who was not involved in this study but who investigates possible FRB scenarios. “Every orbit, there is some energy loss from the system,” he says. “Due to tidal interactions between the planet and the star, the orbit very quickly shrinks.” So it’s possible that the orbit could shrink so fast that FRB signals wouldn’t last long enough for a chance detection, he says.

But the orbit change could also give astronomers a way to check this scenario as an FRB source. Observing repeating FRBs over several years to track any changes in the time between bursts could narrow down whether this hypothesis could explain the observations, Lu says. “That may be a good clue.” More

A chance alignment may have revealed a star from the universe’s first billion years.

If confirmed, this star would be the most distant one ever seen, obliterating the previous record (SN: 7/11/17). Light from the star traveled for about 12.9 billion years on its journey toward Earth, about 4 billion years longer than the former record holder, researchers report in the March 30 Nature. Studying the object could help researchers learn more about the universe’s composition during that early, mysterious time.

“These are the sorts of things that you only hope you could discover,” says astronomer Katherine Whitaker of the University of Massachusetts Amherst, who was not part of the new study.

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The researchers found the object while analyzing Hubble Space Telescope images of dozens of clusters of galaxies nearer to Earth. These clusters are so massive that they bend and focus the light from more distant background objects, what’s known as gravitational lensing (SN: 10/6/15).

In images of one cluster, astronomer Brian Welch of Johns Hopkins University and colleagues noticed a long, thin, red arc. The team realized that the arc was a background galaxy whose light the cluster had warped and amplified.

Atop that red arc is a bright spot that is too small to be a small galaxy or a star cluster, the researchers say. “We stumbled into finding that this was a lensed star,” Welch says.

The researchers estimate that the star’s light originates from only 900 million years after the Big Bang, which took place about 13.8 billion years ago.

Welch and his colleagues think that the object, which they poetically nicknamed “Earendel” from the old English word meaning “morning star” or “rising light,” is a behemoth with at least 50 times the mass of the sun. But the researchers can’t pin down that value, or learn more about the star or even confirm that it is a star, without more detailed observations.

The researchers plan to use the recently launched James Webb Space Telescope to examine Earendel (SN: 10/6/21). The telescope, also known as JWST, will begin studying the distant universe this summer.

JWST may uncover objects from even earlier times in the universe’s history than what Hubble can see because the new telescope will be sensitive to light from more distant objects. Welch hopes that the telescope will find many more of these gravitationally lensed stars. “I’m hoping that this record won’t last very long.” More

Like two great songwriters working side by side and inspiring each other to create their best work, the Magellanic Clouds spawn new stars every time the two galaxies meet.

Visible to the naked eye but best seen from the Southern Hemisphere, the Large and Small Magellanic Clouds are by far the most luminous of the many galaxies orbiting the Milky Way. New observations reveal that on multiple occasions the two bright galaxies have minted a rash of stars simultaneously, researchers report March 25 in Monthly Notices of the Royal Astronomical Society: Letters.

Astronomer Pol Massana at the University of Surrey in England and his colleagues examined the Small Magellanic Cloud. Five peaks in the galaxy’s star formation rate — at 3 billion, 2 billion, 1.1 billion and 450 million years ago and at present — match similarly timed peaks in the Large Magellanic Cloud. That’s a sign that one galaxy triggers star formation in the other whenever the two dance close together.

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“This is the most detailed star formation history that we’ve ever had of the [Magellanic] Clouds,” says Paul Zivick, an astronomer at Texas A&M University in College Station who was not involved in the new work. “It’s painting a very compelling picture that these two have had a very intense set of interactions over the last two to three gigayears.”

Even as the two galaxies orbit the Milky Way at 160,000 and 200,000 light-years from Earth, they also orbit each other (SN: 1/9/20). Their orbit is elliptical, which means they periodically pass near each other. Just as tides from the moon’s gravity stir the seas, tides from one galaxy’s gravity slosh around the other’s gas, inducing star birth, says study coauthor Gurtina Besla, an astrophysicist at the University of Arizona in Tucson.

During the last encounter, which happened 100 million to 200 million years ago, the smaller galaxy probably smashed right through the larger, Besla says, which sparked the current outbreak of star birth. The last star formation peak in the Large Magellanic Cloud occurred only in its northern section, so she says that’s probably where the collision took place.

Based on the star formation peaks, the period between Magellanic encounters has decreased from a billion to half a billion years. Besla attributes this to a process known as dynamical friction. As the Small Magellanic Cloud orbits its mate, it passes through the larger galaxy’s dark halo, attracting a wake of dark matter behind itself. The gravitational pull of this dark matter wake slows the smaller galaxy, shrinking its orbit and reducing how much time it takes to revolve around the Large Magellanic Cloud.

The future for the two galaxies may not be so starry, however. They recently came the closest they’ve ever been to the Milky Way, and its tides, Besla says, have probably yanked the pair apart. If so, the Magellanic Clouds, now separated by 75,000 light-years, may never approach each other again, putting an end to their most productive episodes of star making, just as musicians sometimes flounder after leaving bandmates to embark on solo careers. More

A new analysis of nearly a quarter million stars puts firm ages on the most momentous pages from our galaxy’s life story.

Far grander than most of its neighbors, the Milky Way arose long ago, as lesser galaxies smashed together. Its thick disk — a pancake-shaped population of old stars — originated remarkably soon after the Big Bang and well before most of the stellar halo that envelops the galaxy’s disk, astronomers report March 23 in Nature.

“We are now able to provide a very clear timeline of what happened in the earliest time of our Milky Way,” says astronomer Maosheng Xiang.

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He and Hans-Walter Rix, both at the Max Planck Institute for Astronomy in Heidelberg, Germany, studied almost 250,000 subgiants — stars that are growing larger and cooler after using up the hydrogen fuel at their centers. The temperatures and luminosities of these stars reveal their ages, letting the researchers track how different epochs in galactic history spawned stars with different chemical compositions and orbits around the Milky Way’s center.

“There’s just an incredible amount of information here,” says Rosemary Wyse, an astrophysicist at Johns Hopkins University who was not involved with the study. “We really want to understand how our galaxy came to be the way it is,” she says. “When were the chemical elements of which we are made created?”

Xiang and Rix discovered that the Milky Way’s thick disk got its start about 13 billion years ago. That’s just 800 million years after the universe’s birth. The thick disk, which measures 6,000 light-years from top to bottom in the sun’s vicinity, kept forming stars for a long time, until about 8 billion years ago.

During this period, the thick disk’s iron content shot up 30-fold as exploding stars enriched its star-forming gas, the team found. At the dawn of the thick disk era, a newborn star had only a tenth as much iron, relative to hydrogen, as the sun; by the end, 5 billion years later, a thick disk star was three times richer in iron than the sun.

Xiang and Rix also found a tight relation between a thick disk star’s age and iron content. This means gas was thoroughly mixed throughout the thick disk: As time went on, newborn stars inherited steadily higher amounts of iron, no matter whether the stars formed close to or far from the galactic center.

But that’s not all that was happening. As other researchers reported in 2018, another galaxy once hit our own, giving the Milky Way most of the stars in its halo, which engulfs the disk (SN: 11/1/18). Halo stars have little iron.

The new work revises the date of this great galactic encounter: “We found that the merger happened 11 billion years ago,” Xiang says, a billion years earlier than thought. As the intruder’s gas crashed into the Milky Way’s gas, it triggered the creation of so many new stars that our galaxy’s star formation rate reached a record high 11 billion years ago.

The merger also splashed some thick disk stars up into the halo, which Xiang and Rix identified from the stars’ higher iron abundances. These “splash” stars, the researchers found, are at least 11 billion years old, confirming the date of the merger.

The thick disk ran out of gas 8 billion years ago and stopped making stars. Fresh gas around the Milky Way then settled into a thinner disk, which has given birth to stars ever since — including the 4.6-billion-year-old sun and most of its stellar neighbors. The thin disk is about 2,000 light-years thick in our part of the galaxy.

“The Milky Way has been quite quiet for the last 8 billion years,” Xiang says, experiencing no further encounters with big galaxies. That makes it different from most of its peers.

If the thick disk really existed 13 billion years ago, Xiang says, then the new James Webb Space Telescope (SN: 1/24/22) may discern similar disks in galaxies 13 billion light-years from Earth — portraits of the Milky Way as a young galaxy. More

It’s official: The number of planets known beyond our solar system has just passed 5,000.

The exoplanet census surpassed this milestone with a recent batch of 60 confirmed exoplanets. These additional worlds were found in data from NASA’s now-defunct K2 mission, the “second life” of the prolific Kepler space telescope, and confirmed with new observations, researchers report March 4 at arXiv.org.

As of March 21, these finds put NASA’s official tally of exoplanets at 5,005.

It’s been 30 years since scientists discovered the first planets orbiting another star — an unlikely pair of small worlds huddled around a pulsar (SN: 1/11/92). Today, exoplanets are so common that astronomers expect most stars host at least one (SN: 1/11/12), says astronomer Aurora Kesseli of Caltech.

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“One of the most exciting things that I think has happened in the last 30 years is that we’ve really started to be able to fill out the diversity of exoplanets,” Kesseli says

Some look like Jupiter, some look — perhaps — like Earth and some look like nothing familiar. The 5,005 confirmed exoplanets include nearly 1,500 giant gassy planets, roughly 200 that are small and rocky and almost 1,600 “super-Earths,” which are larger than our solar system’s rocky planets and smaller than Neptune (SN: 8/11/15).

Astronomers can’t say much about those worlds beyond diameters, masses and densities. But several projects, like the James Webb Space Telescope, are working on that, Kesseli says (SN: 1/24/22). “Not only are we going to find tons and tons more exoplanets, but we’re also going to start to be able to actually characterize the planets,” she says.

And the search is far from over. NASA’s newest exoplanet hunter, the TESS mission, has confirmed more than 200 planets, with thousands more yet to verify, Kesseli says (SN: 12/2/21). Ongoing searches from ground-based telescopes keep adding to the count as well.

“There’s tons of exoplanets out there,” Kesseli says, “and even more waiting to be discovered.” More

Coronal loops, well-defined hot strands of plasma that arch out into the sun’s atmosphere, are iconic to the sun’s imagery. But many of the supposed coronal loops we see might not be there at all.    

Some coronal loops might be an illusion created by “wrinkles” of greater density in a curtain of plasma dubbed the coronal veil, researchers propose March 2 in Astrophysical Journal. If true, the finding, sparked by unexpected plasma structures seen in computer simulations of the sun’s atmosphere, may change how scientists go about measuring some properties of our star.

“It’s kind of inspiring to see these detailed structures,” says Markus Aschwanden, an astrophysicist at Lockheed Martin’s Solar & Astrophysics Lab in Palo Alto, Calif., who was not involved in the study. “They are so different than what we anticipated.”

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Scientists have begun to develop a better understanding of the sun’s complex atmosphere, or corona, only in the last few years (SN: 12/19/17). Coronal loops have been used to measure many properties of the corona, including temperature and density, and they may be key to figuring out why the sun’s atmosphere is so much hotter than its surface (SN: 8/20/17). But astronomers have long wondered just how the loops appear to be so orderly when they originate in the sun’s turbulent surface (SN: 8/17/17).     

So solar physicist Anna Malanushenko and her colleagues attempted to isolate individual coronal loops in 3-D computer simulations originally developed to simulate the life cycle of a solar flare. The team expected to see neatly oriented strands of plasma, because coronal loops appear to align themselves to the sun’s magnetic field, like metal shavings around a bar magnet.

Instead, the plasma appeared as a curtainlike structure winding out from the sun’s surface that folded in on itself like a wrinkled sheet. In the simulation, many of the supposed coronal loops turned out to not be real objects. While there were structures along the magnetic fields, they were neither thin nor compact as expected. They more closely resembled clouds of smoke. As the team changed the point of view from which they looked at these wrinkles in the veil in the simulation, their shape and orientation changed. And from certain viewing angles, the wrinkles resembled coronal loops.

The observations were mind-blowing, says Malanushenko, of the National Center for Atmospheric Research in Boulder, Colo. “The traditional thought was that if we see this arching coronal loop that there is a garden hose–like strand of plasma.” The structure in the simulation was much more complex and displayed complicated boundaries and a raggedy structure.

Still, not all coronal loops are necessarily illusions within a coronal veil. “We don’t know which ones are real and which ones are not,” Malanushenko says. “And we absolutely need to be able to tell to study the solar atmosphere.”

It’s also not clear how the purported coronal veil might impact previous analyses of the solar atmosphere. “On one hand, this is depressing,” Malanushenko says of the way the new findings cast doubt on previous understandings. On the other hand, she finds the uncertainty exciting. Astronomers will need to develop a way to observe the veil and confirm its existence. “Whenever we develop new methods, we open the door for new knowledge.” More

The nearest black hole to Earth isn’t a black hole at all. Instead, what scientists thought was a stellar triplet — two stars and a black hole — is actually a pair of stars caught in a unique stage of evolution.

In May 2020, a team of astronomers reported that the star system HR 6819 was probably made up of a bright, massive star locked in a tight, 40-day orbit with a nonfeeding, invisible black hole plus a second star orbiting farther away. At about 1,000 light-years from Earth, that would make this black hole the nearest to us (SN: 5/6/20). But over the following months, other teams analyzed the same data and came to a different conclusion: The system hosts only two stars and no black hole.

Now, the original team and one of the follow-up teams have joined forces and looked at HR 6819 with more powerful telescopes that collect a different type of data. The new data can make out finer details on the sky, allowing the astronomers to definitively see how many objects are in the system and what type of objects they are, the teams report in the March Astronomy & Astrophysics.

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“Ultimately, it was the binary system that best explains everything,” says astronomer Abigail Frost of KU Leuven in Belgium.

Previous observations of HR 6819 showed it as a unit, so astronomers couldn’t differentiate the objects in the system nor their masses. To nail down HR 6819’s true nature, Frost and colleagues turned to the Very Large Telescope Array, a network of four interconnected telescopes in Chile that can essentially see the separate stars.

“It allowed us to disentangle that original signal definitively, which is really important to determine how many stars were in it, and whether one of them was a black hole,” Frost says.

The scientists think one of the stars is a massive bright blue star that has been siphoning material from its companion star’s bloated atmosphere. That companion star now has little gaseous atmosphere left. “It’s already gone through its main life, but because the outside has been stripped off, and you only see the exposed core, it has similar temperature and luminosity and radius to a young star,” says Kareem El-Badry, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. El-Badry was not involved in the new study, but he suggested in 2021 that HR 6819 is a binary system.

This siphoned star’s core color and brightness could fool astronomers looking at the older data into thinking it was a young star with 10 times as much mass. It originally appeared as though this star was orbiting something massive but invisible — a black hole.

Once the researchers unraveled the system’s details, they realized this system is a unique one, showing astronomers a phase not seen before among systems with massive stars. “It is a missing link in binary star evolution,” says astrophysicist Maxwell Moe of the University of Arizona in Tucson, who was also not part of the new study.

Astronomers for years have seen binary systems where one star is actively pulling gas off the other, and they’ve seen systems where the donor star is just a naked stellar core. But in HR 6819, the donor star has stopped giving mass to the other. “It still has a little bit of envelope left but is quickly contracting, evolving to become a remnant core,” Moe says.

Frost and her colleagues are using the Very Large Telescope Array to monitor HR 6819 over a year to track precisely how the stars are moving. “We want to really understand how the individual stars in the system are ticking,” she says. The team will then use that information in computer simulations of binary star evolution. “[It’s] exciting to now have a system that we can use as kind of a cornerstone to investigate this in more detail,” Frost says.

Even though HR 6819 doesn’t have the nearest black hole to Earth, it appears to have something more useful to astronomers. More

Huge rings of gas surround a large red star named V Hydrae, new images show, signaling its eventual transformation into a much smaller and bluer star.

“It’s definitely going through its metamorphosis,” says Raghvendra Sahai, an astronomer at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Such ringlike structures have never been seen in any object like this before.”

Observations of the three concentric rings, all ejected from the star during the last 800 years, could help astronomers understand how giant stars lose mass toward the end of their lives and seed the cosmos with planet- and life-building elements.

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Born roughly twice as massive as the sun and lying about 1,300 light-years from Earth, V Hydrae is what’s known as an asymptotic giant branch star. It once fused hydrogen in its core, as the sun does. But now it is a cool, brilliant, puffed-up star that alternately burns hydrogen and helium in shells around a carbon-oxygen core. Such stars cast lots of material into space.

“The processes by which this happens are not well-understood,” says Sahai, who has studied V Hydrae since the 1980s.

His team used the Atacama Large Millimeter/submillimeter Array of radio telescopes in Chile, also known as ALMA, to detect the three rings of gas. Beyond them lie three additional rings, which are fainter and seen only partially, Sahai and colleagues report in a paper submitted February 18 at arXiv.org.

The outermost complete ring now sits about 260 billion kilometers from the star, or 1,740 times as far as Earth is from the sun — more than 40 times Pluto’s distance from Earth. By measuring the speed at which the three complete rings are moving outward and their current distances from the star, the astronomers calculate that it cast them off about 270, 485 and 780 years ago.

It’s thought that another star orbits the main one every few hundred years on an elliptical orbit. When the companion dives in, it can trigger the giant star to cast more material into space, the team says.

The new image is striking and unusual, and it illustrates how a companion star enhances a giant star’s loss of mass, says Joel Kastner, an astronomer at the Rochester Institute of Technology in New York who was not part of the study. “Mass loss is very important because it’s how the elements of life get distributed from stars into the universe.”

Stars like V Hydrae forged most of the nitrogen in Earth’s air as well as much of our planet’s carbon, the basis for all terrestrial life (SN: 2/12/21; SN: 11/18/21). V Hydrae has so many carbon compounds in its atmosphere that it’s classified as a carbon star. It’s also one of the reddest stars known because those compounds as well as dust particles absorb its blue and violet light.

Sahai expects the star’s ejection of material to continue, but, he says, “it’s anybody’s guess as to how many more rings will be produced.”

When the star loses all of its atmosphere, probably many thousands of years from now, it will expose its hot core, whose ultraviolet light will set the cast-off material aglow, creating a beautiful bubble of gas known as a planetary nebula.

When the nebula dissipates, all that will remain of the magnificent red star will be a tiny blue one — a white dwarf — a little larger than Earth, plus innumerable life-giving elements floating through the Milky Way. More