Astronomy

There’s a new addition to astronomers’ portrait gallery of black holes. 

Astronomers announced May 12 that they have finally assembled an image of the supermassive black hole at the center of our galaxy. 

“This image shows a bright ring surrounding the darkness, the telltale sign of the shadow of the black hole,” astrophysicist Feryal Özel of the University of Arizona in Tucson said at a news conference announcing the result.

The black hole, known as Sagittarius A*, appears as a faint silhouette amidst the glowing material that surrounds it. The image reveals the turbulent, twisting region immediately surrounding the black hole in new detail. The findings also were published May 12 in 6 studies in the Astrophysical Journal Letters.

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A planet-spanning network of radio telescopes, known as the Event Horizon Telescope, worked together to create this much-anticipated look at the Milky Way’s giant. Three years ago, the same team released the first-ever image of a supermassive black hole (SN: 4/10/19). That object sits at the center of the galaxy M87, about 55 million light-years from Earth. 

But Sagittarius A*, or Sgr A* for short, is “humanity’s black hole,” says astrophysicist Sera Markoff of the University of Amsterdam, and a member of the EHT collaboration. 

At 27,000 light-years away, the behemoth is the closest giant black hole to Earth. That proximity means that Sgr A* is the most-studied supermassive black hole in the universe. Yet Sgr A* and others like it remain some of the most mysterious objects ever found. 

That’s because, like all black holes, Sgr A* is an object so dense that its gravitational pull won’t let light escape. Black holes are “natural keepers of their own secrets,” says physicist Lena Murchikova of the Institute for Advanced Study in Princeton, N.J., who is not part of the EHT team. Their gravity traps light that falls within a border called the event horizon. EHT’s images of Sgr A* and the M87 black hole skirt up to that inescapable edge.

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This sonification is a translation into sound of the Event Horizon Telescope’s image of the supermassive black hole Sagittarius A*. The sonification sweeps clockwise around the black hole image. Material closer to the black hole orbits faster than material farther away. Here, the faster-moving material is heard at higher frequencies. Very low tones represent material outside the black hole’s main ring. Louder volume indicates brighter spots in the image.

Sgr A* feeds on hot material pushed off of massive stars at the galactic center. That gas, drawn toward Sgr A* by its gravitational pull, flows into a surrounding disk of glowing material, called an accretion disk. The disk, the stars and an outer bubble of X-ray light “are like an ecosystem,” says astrophysicist Daryl Haggard of McGill University in Montreal and a member of the EHT collaboration. “They’re completely tied together.”

That accretion disk is where the action is — as the gas moves within immensely strong magnetic fields — so astronomers want to know more about how the disk works.

Like the majority of supermassive black holes,  Sgr A* is quiet and faint (SN: 6/5/19 ). The black hole eats only a few morsels fed to it by its accretion disk. Still, “it’s always been a little bit of a puzzle why it’s so, so faint,” says astrophysicist Meg Urry of Yale University, who is not part of the EHT collaboration. M87’s black hole, in comparison, is a monster gorging on nearby material and shooting out enormous, powerful jets (SN: 11/10/21). But that doesn’t mean Sgr A* isn’t producing light. Astrophysicists have seen its region feebly glowing in radio waves, jittering in infrared and burping in X-rays.

In fact, the accretion disk around Sgr A* seems to constantly flicker and simmer. This variability, the constant flickering, is like a froth on top of ocean waves, Markoff says. “​​And so we’re seeing this froth that is coming up from all this activity, and we’re trying to understand the waves underneath the froth.” 

The big question, she adds, has been if astronomers would be able to see something changing in those waves with EHT. In the new work, they’ve seen hints of those changes below the froth, but the full analysis is still ongoing.

By combining about 3.5 petabytes of data, or the equivalent of about 100 million TikTok videos, captured in April 2017, researchers could begin to piece together the picture. To tease out an image from the initial massive jumble of data, the EHT team needed years of work, complicated computer simulations and observations in various types of light from other telescopes. 

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Scientists created a vast library of computer simulations of Sagittarius A* (one shown) to explore the turbulent flow of hot gas that rings the black hole. That rapid flow causes the ring’s appearance to vary in brightness on timescales of minutes. Scientists compared these simulations with the newly released observations of the black hole to better understand its true properties.

Those “multiwavelength” data from the other telescopes were crucial to assembling the image. “By looking at these things simultaneously and all together, we’re able to come up with a complete picture,” says theorist Gibwa Musoke of the University of Amsterdam. 

Sgr A*’s variability, the constant simmering, complicated the analysis because the black hole changes on timescales of just a few minutes, changing as the researchers were imaging it. “It was like trying to take a clear picture of a running child at night,” astronomer José L. Gómez of Instituto de Astrofísica de Andalucía in Granada, Spain, said at a news conference announcing the result. M87 was easier to analyze because it changed over the course of weeks.

Ultimately, a better understanding of what is happening in the disk so close to Sgr A* could help scientists learn how many other similar supermassive black holes work. 

The new EHT observations also confirm the mass of Sgr A* at 4 million times that of the sun. If the black hole replaced our sun, the shadow EHT imaged would sit within Mercury’s orbit. 

The researchers also used the image of Sgr A* to put general relativity to the test (SN: 2/3/21). Einstein’s steadfast theory of gravity passed: The size of the shadow matched the predictions of general relativity. By testing the theory in extreme conditions — like those around black holes — scientists hope to pinpoint any hidden weaknesses.

Scientists have previously tested general relativity by following the motions of stars that orbit very close to Sgr A* — work that also helped confirm that the object truly is a black hole (SN: 7/26/18). For that discovery, researchers Andrea Ghez and Reinhard Genzel won a share of the Nobel Prize in physics in 2020 (SN: 10/6/20).

The two types of tests of general relativity are complementary,  says astrophysicist Tuan Do of UCLA. “With these big physics tests, you don’t want to use just one method.” If one test appears to contradict general relativity, scientists can check for a corresponding discrepancy in the other.

The Event Horizon Telescope, however, tests general relativity much nearer to the black hole’s edge, which could highlight subtle effects of physics beyond general relativity. “The closer you get, the better you are in terms of being able to look for these effects,” says physicist Clifford Will of the University of Florida in Gainesville.

However, some researchers have criticized a similar test of general relativity made using the EHT image of M87’s black hole (SN: 10/1/20). That’s because the test relies on relatively shaky assumptions about the physics of how material swirls around a black hole, says physicist Sam Gralla of the University of Arizona in Tucson. Testing general relativity in this way “would only make sense if general relativity were the weakest link,” but scientists’ confidence in general relativity is stronger than the assumptions that went into the test, he says.

The observations of Sgr A* provide more evidence that the object is in fact a black hole, says physicist Nicolas Yunes of the University of Illinois Urbana-Champaign. “It’s really exciting to have the first image of a black hole that is in our own Milky Way. It’s fantastic.” It sparks the imagination, like early pictures astronauts took of Earth from the moon, he says.

This won’t be the last eye-catching image of Sgr A* from EHT. Additional observations, made in 2018, 2021 and 2022, are still waiting to be analyzed. 

“This is our closest supermassive black hole,” Haggard says. “It is like our closest friend and neighbor. And we’ve been studying it for years as a community. [This image is a] really profound addition to this exciting black hole we’ve all kind of fallen in love with in our careers.” More

In the solar system’s early years, the still-forming giant planets sidestepped, did a do-si-do and then swung one of their partners away from the sun’s gravitational grasp. Things settled, and our planetary system was in its final configuration.

What triggered that planetary shuffle has been unknown. Now, computer simulations suggest that the hot radiation of the young sun evaporating its planet-forming disk of gas and dust led to the scrambling of the giant planets’ orbits, researchers report in the April 28 Nature.

As a result, the four largest planets may have been in their final configuration within 10 million years of the solar system’s birth about 4.6 billion years ago. That’s much quicker than the 500 million years that previous work had suggested.

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The planetary-shuffling mechanism that the team uncovered in the computer simulations is very innovative, says Nelson Ndugu, an astrophysicist who studies forming planetary systems at North-West University in Potchefstroom, South Africa, and Muni University in Arua, Uganda. “It has huge potential.”

Heaps of evidence, including observations of extrasolar planetary systems forming (SN: 7/2/18), had already indicated that something in our solar system’s early history jumbled the giant planets’ orbits, which scientists call the giant-planet instability (SN: 5/25/05).

“The evidence for the giant-planet instability is really robust,” says Seth Jacobson, a planetary scientist at Michigan State University in East Lansing. “It explains many features of the outer solar system,” he says, like the large number of rocky objects beyond Neptune that make up the Kuiper Belt (SN: 12/31/09).

To figure out what triggered that instability, Jacobson and colleagues ran computer simulations of the thousands of ways that the early solar system could have developed. All started with a young star and a planet-forming disk of gas and dust surrounding the star. The team then altered the disk parameters, such as its mass, density and how fast it evolved.

The simulations also included the still-forming giant planets — five of them, in fact. Astronomers think a third ice giant, in addition to Uranus and Neptune, was originally a solar system member (SN: 4/20/12). Jupiter and Saturn round out the final tally of these massive planets.

When the sun officially became a star, that is, the moment it began burning hydrogen at its core — roughly 4.6 billion years ago — its ultraviolet emission would have hit the disk’s gas, ionizing it and heating it to tens of thousands of degrees. “This is a very well-documented process,” Jacobson says. As the gas heats, it expands and flows away from the star, beginning with the inner portion of the disk.

“The disk disperses its gas from inside out,” says Beibei Liu, an astrophysicist at Zhejiang University in Hangzhou, China. He and Jacobson collaborated with astronomer Sean Raymond of Laboratoire d’Astrophysique de Bordeaux in France in the new research.

In the team’s simulations, as the inner part of the disk dissolves, that area loses mass, so the embedded, still-forming planets feel less gravity from that region, Jacobson says. But the planets still feel the same amount of pull from the disk’s outer region. This gravitational torquing, as the team calls it, can trigger a rebound effect: “Originally, the planets migrate in, and they reach the [inner] edge of this disk, and they reverse their migration,” Liu says.

Because of Jupiter’s large mass, it’s mostly unaffected. Saturn, though, moves outward and into the region, which, in the simulations, holds the three ice giant planets. That area becomes crowded, Liu says, and close planetary interactions follow. One ice giant gets kicked out of the solar system entirely, Uranus and Neptune shift a bit farther from the sun, and “they gradually form the orbits close to our solar system’s configuration,” Liu says.

In their computer simulations, the researchers found that as the sun’s radiation evaporates the disk, a planetary reshuffle nearly always ensues. “We can’t avoid this instability,” Jacobson says.

Now that the researchers have an idea of what may have caused this solar system shuffle, the next step is to simulate how the evaporation of the disk could affect other objects.

“We’ve focused really heavily on the giant planets, because their orbits were the original motivation,” Jacobson says. “But now, we have to do the follow-up work to show how this trigger mechanism relates to the small bodies.” More

If you’re an aspiring life-form, you might want to steer clear of planets around orange dwarf stars.

Some astronomers have called these orange suns “Goldilocks stars” (SN: 11/18/09). They are dimmer and age more slowly than yellow sunlike stars, thus offering an orbiting planet a more stable climate. But they are brighter and age faster than red dwarfs, which often spew large flares. However, new observations show that orange dwarfs emit lots of ultraviolet light long after birth, potentially endangering planetary atmospheres, researchers report in a paper submitted March 29 at arXiv.org.

Using data from the Hubble Space Telescope, astronomer Tyler Richey-Yowell and her colleagues examined 39 orange dwarfs. Most are moving together through the Milky Way in two separate groups, either 40 million or 650 million years old.

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To Richey-Yowell’s surprise, she and her team found that the ultraviolet flux didn’t drop off from the younger orange stars to the older ones — unlike the case for yellow and red stars. “I was like, `What the heck is going on?’” says Richey-Yowell, of Arizona State University in Tempe.

In a stroke of luck, another team of researchers supplied part of the answer. As yellow sunlike stars age, they spin more slowly, causing them to be less active and emit less UV radiation. But for orange dwarfs, this steady spin-down stalls when the stars are roughly a billion years old, astronomer Jason Lee Curtis at Columbia University and colleagues reported in 2019.

“[Orange] stars are just much more active for a longer time than we thought they were,” Richey-Yowell says. That means these possibly not-so-Goldilocks stars probably maintain high levels of UV light for more than a billion years.

And that puts any potential life-forms inhabiting orbiting planets on notice. Far-ultraviolet light — whose photons, or particles of light, have much more energy than the UV photons that give you vitamin D — tears molecules in a planet’s atmosphere apart. That leaves behind individual atoms and electrically charged atoms and groups of atoms known as ions. Then the star’s wind — its outflow of particles — can carry the ions away, stripping the planet of its air.

But not all hope is lost for aspiring life-forms that have an orange dwarf sun. Prolonged exposure to far-ultraviolet light can stress planets but doesn’t necessarily doom them to be barren, says Ed Guinan, an astronomer at Villanova University in Pennsylvania who was not involved in the new work. “As long as the planet has a strong magnetic field, you’re more or less OK,” he says.

Though far-ultraviolet light splits water and other molecules in a planet’s atmosphere, the star’s wind can’t remove the resulting ions if a magnetic field as strong as Earth’s protects them. “That’s why the Earth survived” as a life-bearing world, Guinan says. In contrast, Venus might never have had a magnetic field, and Mars lost its magnetic field early on and most of its air soon after.

“If the planet doesn’t have a magnetic field or has a weak one,” Guinan says, “the game is over.”

What’s needed, Richey-Yowell says, is a study of older orange dwarfs to see exactly when their UV output declines. That will be a challenge, though. The easiest way to find stars of known age is to study a cluster of stars, but most star clusters get ripped apart well before their billionth birthday (SN: 7/24/20). As a result, star clusters somewhat older than this age are rare, which means the nearest examples are distant and harder to observe. More

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