Just some of the visible matter in Tucana.Image: ESA/Hubble & NASA (Fair Use)
Some 163,000 light-years from the Milky Way is a much smaller, much more ancient galaxy: Tucana II, so named for the tropical bird-resembling constellation in which it sits. Sitting at the periphery of our galaxy’s gravitational pull, Tucana II provides researchers with the opportunity to understand the composition of the earliest galactic structures in the universe.
Now, a team of astronomers has found evidence of an extended dark matter halo around the galaxy. Their research was published today in the journal Nature Astronomy.
“We know [dark matter] is there because in order for galaxies to remain bound, there must be more matter than what we see visibly, from starlight,” said Anirudh Chiti, an astronomer at the Massachusetts Institute of Technology, in a phone call. “That led to the hypothesis of dark matter existing as an ingredient that holds galaxies together; without it, galaxies that we know, or at least of the stuff at their outskirts, would just fly apart.”
The Tucana dwarf galaxy, imaged by the Hubble Space Telescope.Image: Hubble (Fair Use)
A dark matter halo is a region of gravitationally bound matter in space. (The dark matter halo of the Milky Way extends far beyond the pinwheel that constitutes our galaxy’s visible stuff). The team found that the gravitational bounds of Tucana II are between three and five times more massive than previously thought, showing that even some of the oldest galaxies will have dark matter halos.
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Tucana II happens to be the most chemically primitive galaxy that we currently know, meaning that some of its stars have very low metal content (the universe’s heavier elements were produced later in time). The team realized that Tucana II had the dark matter halo when observations of stars in that region of the sky revealed that the stars were moving in tandem.
“If you just look at the region of the sky where the galaxy exists, you don’t actually see a clustering or overdensity of stars,” Chiti, who is lead author of the recent paper, said. “It’s only when you look at their velocities and realize it’s a group of stars moving at the same velocity that you realize that there’s a galaxy that exists there.”
As study co-author Anna Frebel, also an astronomer at MIT, put it in a university press release, the whorl of Tucana II’s movement resembles “bathwater going down the drain.” Compellingly, some of the galaxy’s peripheral stars are older than stars closer to the galactic center. The team hypothesizes that Tucana II may be the result of a previous galactic merger, a cosmic clash that saw one primitive galaxy consumed by another, resulting in stars of different origins in the same galaxy.
Whether or not that theory of Tucana II’s origin holds true, a similar collision is certainly in its future. Since it’s within the gravitational realm of the much-more-massive Milky Way, eventually, the relatively petite galaxy will be swallowed up by our own.
While astronomers know how to spot dark matter halos, they still don’t know exactly what dark matter is. Besides finding its halos around galaxies, researchers are also looking for dark matter’s identity in mysterious signals from neutron stars and in the form of tiny, theoretical black holes.
Artist’s impression of the active magnetar Swift J1818.0-1607. Credit: Carl Knox, OzGrav.
Astronomers from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and CSIRO have just observed bizarre, never-seen-before behavior from a radio-loud magnetar—a rare type of neutron star and one of the strongest magnets in the universe.
Their new findings, published today in the Monthly Notices of the Royal Astronomical Society (MNRAS), suggest magnetars have more complex magnetic fields than previously thought, which may challenge theories of how they are born and evolve over time.
Magnetars are a rare type of rotating neutron star with some of the most powerful magnetic fields in the universe. Astronomers have detected only 30 of these objects in and around the Milky Way—most of them detected by X-ray telescopes following a high-energy outburst.
However, a handful of these magnetars have also been seen to emit radio pulses similar to pulsars—the less-magnetic cousins of magnetars that produce beams of radio waves from their magnetic poles. Tracking how the pulses from these radio-loud magnetars change over time offers a unique window into their evolution and geometry.
In March 2020, a new magnetar named Swift J1818.0-1607 (J1818 for short) was discovered after it emitted a bright X-ray burst. Rapid follow-up observations detected radio pulses originating from the magnetar. Curiously, the appearance of the radio pulses from J1818 were quite different from those detected from other radio-loud magnetars.
Most radio pulses from magnetars maintain a consistent brightness across a wide range of observing frequencies. However, the pulses from J1818 were much brighter at low frequencies than high frequencies—similar to what is seen in pulsars, another more common type of radio-emitting neutron star.
In order to better understand how J1818 would evolve over time, a team led by scientists from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) observed it eight times using the CSIRO Parkes radio telescope (also known as Murriyang) between May and October 2020.
During this time, they found the magnetar underwent a brief identity crisis: In May it was still emitting the unusual pulsar-like pulses that had been detected previously; however, by June, it had started flickering between a bright and a weak state. This flickering behavior reached a peak in July, when the astronomers saw it flickering back and forth between pulsar-like and magnetar-like radio pulses.
“This bizarre behavior has never been seen before in any other radio-loud magnetar,” explains study lead author and Swinburne University/CSIRO Ph.D. student Marcus Lower. “It appears to have only been a short-lived phenomenon, as by our next observation, it had settled permanently into this new magnetar-like state.”
The scientists also looked for pulse shape and brightness changes at different radio frequencies and compared their observations to a 50-year-old theoretical model. This model predicts the expected geometry of a pulsar, based on the twisting direction of its polarized light.
“From our observations, we found that the magnetic axis of J1818 isn’t aligned with its rotation axis,” says Lower. “Instead, the radio-emitting magnetic pole appears to be in its southern hemisphere, located just below the equator. Most other magnetars have magnetic fields that are aligned with their spin axes or are a little ambiguous. This is the first time we have definitively seen a magnetar with a misaligned magnetic pole.”
Remarkably, this magnetic geometry appears to be stable over most observations. This suggests any changes in the pulse profile are simply due to variations in the height the radio pulses are emitted above the neutron star surface. However, the August 1st 2020 observation stands out as a curious exception.
“Our best geometric model for this date suggests that the radio beam briefly flipped over to a completely different magnetic pole located in the northern hemisphere of the magnetar,” says Lower.
A distinct lack of any changes in the magnetar’s pulse profile shape indicate the same magnetic field lines that trigger the ‘normal’ radio pulses must also be responsible for the pulses seen from the other magnetic pole.
The study suggests this is evidence that the radio pulses from J1818 originate from loops of magnetic field lines connecting two closely spaced poles, like those seen connecting the two poles of a horseshoe magnet or sunspots on the sun. This is unlike most ordinary neutron stars, which are expected to have north and south poles on opposite sides of the star that are connected by a donut-shaped magnetic field.
This peculiar magnetic field configuration is also supported by an independent study of the X-rays pulses from J1818 that were detected by the NICER telescope on board the International Space Station. The X-rays appear to come from either a single distorted region of magnetic field lines that emerge from the magnetar surface or two smaller, but closely spaced, regions.
These discoveries have potential implications for computer simulations of how magnetars are born and evolve over long periods of time, as more complex magnetic field geometries will change how quickly their magnetic fields are expected to decay over time. Additionally, theories that suggest fast radio bursts can originate from magnetars will have to account for radio pulses potentially originating from multiple active sites within their magnetic fields.
Catching a flip between magnetic poles in action could also afford the first opportunity to map the magnetic field of a magnetar.
“The Parkes telescope will be watching the magnetar closely over the next year” says scientist and study co-author Simon Johnston, from the CSIRO Astronomy and Space Science.
Mysterious spinning neutron star detected in the Milky Way proves to be an extremely rare discovery
More information:
M E Lower et al. The dynamic magnetosphere of Swift J1818.0−1607, Monthly Notices of the Royal Astronomical Society (2020). DOI: 10.1093/mnras/staa3789
Marcus E. Lower, et al. The dynamic magnetosphere of Swift J1818.0−1607 arxiv.org/abs/2011.12463 arXiv:2011.12463v2 [astro-ph.HE] T
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Astronomers spot bizarre, never-before-seen activity from one of the strongest magnets in the universe (2021, February 1)
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Can you picture Jupiter without any observable clouds or haze? It isn’t easy since Jupiter’s latitudinal cloud bands and its Great Red Spot are iconic visual features in our Solar System. Those features are caused by upswelling and descending gas, mostly ammonia. After Saturn’s rings, Jupiter’s cloud forms are probably the most recognizable feature in the Solar System.
Now astronomers with the Center for Astrophysics | Harvard & Smithsonian (CfA) have found a planet similar in mass to Jupiter, but with a cloud-free atmosphere.
These planets are scarce, and astronomers think only about 7% of exoplanets are like this. The discovery allows scientists to study how they form. Without clouds in the way, a clearer view awaits.
The team of astronomers behind the finding published their results in The Astrophysical Journal Letters. The title is “Evidence of a Clear Atmosphere for WASP-62b: The Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone.” Lead author of the study is Munazza Alam, a grad student at the CfA.
WASP-62b is the nearest planet to WASP-62, a main-sequence star almost 600 light-years from Earth. 62b is the only planet in the system. It’s just over half as massive as Jupiter, and orbits WASP-62 in about 4.5 days. It’s about 1.4 times as large as Jupiter. It falls squarely into the category of Hot Jupiters, with an average temperature of about 1330 K (1057 C; 1934 F.)
Can you picture Jupiter without clouds? We can’t either. Image Credit: Hubble/NASA/ESA
The planet’s temperature, size, and density properties aren’t rare. What’s rare is the cloudlessness of its atmosphere. And the exoplanet’s atmosphere is of special interest to lead author Alam. In a press release, Alam said, “For my thesis, I have been working on exoplanet characterization. I take discovered planets, and I follow up on them to characterize their atmospheres.”
The WASP name comes from the Wide Angle Search for Planets (WASP) South. The planet was first discovered in 2012 and was one of seven Hot Jupiters found at the same time.
WASP-62b was discovered with WASP, but Alam and her colleagues used the Hubble to study it more closely. “I’ll admit that at first, I wasn’t too excited about this planet,” Alam said. “But once I started to take a look at the data, I got excited.”
Using spectroscopy, they watched closely as the planet transited in front of its star three times, looking for potassium and sodium. As the starlight passed through the planet’s atmosphere they identified sodium’s complete spectroscopic signature, but no potassium. The sodium signature told them that the atmosphere was clear.
“This is smoking gun evidence that we are seeing a clear atmosphere,” Alam said.
A screenshot of WASP-62b from NASA’s Eyes on Exoplanets website. Image Credit: NASA
In an email exchange with Universe Today, Alam elaborated on the team’s spectroscopic findings and what they mean.
The focus on potassium and sodium is based on a couple of things. First of all, their spectra are easily observable in optical light. “Sodium and potassium are two species that are readily observable in exoplanet atmosphere observations taken at optical wavelengths, and their presence or absence can help us infer if there are clouds or hazes in an exoplanet’s atmosphere,” Alam said.
Sodium and potassium also play a role in exoplanet atmospheres, though the details aren’t clear. “Sodium and potassium are two elements that play an interesting – yet not well understood – role in the atmospheric physics and chemistry of exoplanets,” Alam explained. She also mentioned that sodium was the first absorption feature identified in an exoplanet’s atmosphere.
The detection of sodium’s complete spectroscopic signature tells astronomers that the atmosphere is clear, even if there’s no way to see the atmosphere. “Clouds in a planet’s atmosphere will mask or obscure parts of the absorption line,” Alam explained. “In the absence of clouds, we can resolve the full sodium signature – which has a tent-like shape with a peak at the core of the absorption feature and broad line wings. For our observations of WASP-62b, this is the second time that we’ve observed the full sodium feature (i.e., with its line wings) in an exoplanet and the first time that we’ve done so from space.”
This figure from the study shows the Hubble Space Telescope Imaging Spectrograph data for WASP-62b and the only other known exoplanet with a clear atmosphere, WASP-96b. Both exoplanets show the “…prominent pressure-broadened wings of the Na D-lines at 0.59 ?m.” Seeing the sodium spectrum with wings indicates that both planets have clear atmospheres. WASP-96b also shows the presence of lithium and potassium. Image Credit: Alam et al, 2021.
But the complete sodium signature does more than tell us that the exoplanet’s atmosphere is cloud-free. It can help explain how much sodium there is and indicate what other elements are in the atmosphere.
“Not only does it tell us that the atmosphere is clear, it can also help us to constrain really precise abundances (quantities) of sodium – as well as other elements that are present in the planet’s atmosphere,” Alam said. “These abundances are useful for measuring key quantities that can help us trace back the origins and evolution of this planet.”
There’s clearly something different going on when a cloud-free planet forms. Since there are so few of them, astronomers are only at the beginning of studying them. The only other cloud-free exoplanet that we know of is the hot Saturn named WASP-96b, found in 2018.
It’ll be up to the James Webb Space Telescope to examine this exoplanet’s atmosphere more closely. And its clear skies make that prospect even more exciting. The Webb’s advanced observing capabilities mean it should be able to identify even more of the chemical constituents in WASP-62b’s atmosphere.
“In preparation for JWST, identifying targets that are cloud-free/haze-free is important for mobilizing community efforts to observe the best planets for detailed atmospheric follow-up.”
From “Evidence of a Clear Atmosphere for WASP-62b: The Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone.”
Due to JWST’s orientation and position in space, it’ll have two small continuous viewing zones (CVZ). They’re centred on each pole of the ecliptic. Fortune is smiling on Alam and other exoplanet scientists because WASP-62b is in one of Webb’s CVZs.
James Webb’s field of view contains two continuous viewing zones, indicated by ovals in the image. The rest of the JWST’s field of regard sweeps through the sky over time. As luck would have it, WASP-62b is in one of JWST’s CVZs. Image Credit: NASA/JWST.
The team of researchers even predicted what the JWST might find in 62b’s atmosphere. In their paper they write “We predict that JWST observations of WASP-62b, within the scope of the ERS program, can conclusively detect Na (12.1?), H2O (35.6?), FeH (22.5?), SiH (6.3?), NH3 (11.1?), CO (8.1?), CO2 (9.7?), and CH4 (3.6?).” They also say that the JWST can offer precise constraints on the abundance of chemicals in the atmosphere.
As part of their work, and to help make the case for follow-up observations with the Webb, the team predicted what the Webb might find. Image Credit: Alam et al, 2021.
In their conclusion, the authors make their case for follow-up observations of WASP-62b with the JWST.
“In preparation for JWST, identifying targets that are cloud-free/haze-free is important for mobilizing community efforts to observe the best planets for detailed atmospheric follow-up. Although alternative targets have since been put forward, WASP-62 is the only star in the JWST CVZ with a known transiting giant planet that is bright enough for high-quality atmospheric characterization via transit spectroscopy.”
The James Webb Space Telescope is scheduled to launch at the end of October 2021.
When black holes swallow down massive amounts of matter from the space around them, they’re not exactly subtle about it. They belch out tremendous flares of X-rays, generated by the material heating to intense temperatures as it’s sucked towards the black hole, so bright we can detect them from Earth.
This is normal black hole behaviour. What isn’t normal is for those X-ray flares to spew forth with clockwork regularity, a puzzling behaviour reported in 2019 from a supermassive black hole at the centre of a galaxy 250 million light-years away. Every nine hours, boom – X-ray flare.
After careful study, astronomer Andrew King of the University of Leicester in the UK identified a potential cause – a dead star that’s endured its brush with a black hole, trapped on a nine-hour, elliptical orbit around it. Every close pass, or periastron, the black hole slurps up more of the star’s material.
“This white dwarf is locked into an elliptical orbit close to the black hole, orbiting every nine hours,” King explained back in April 2020.
“At its closest approach, about 15 times the radius of the black hole’s event horizon, gas is pulled off the star into an accretion disk around the black hole, releasing X-rays, which the two spacecraft are detecting.”
The black hole is the nucleus of a galaxy called GSN 069, and it’s pretty lightweight as far as supermassive black holes go – only 400,000 times the mass of the Sun. Even so, it’s active, surrounded by a hot disc of accretion material, feeding into and growing the black hole.
According to King’s model, this black hole was just hanging out, doing its active accretion thing, when a red giant star – the final evolutionary stages of a Sun-like star – happened to wander a little too close.
The black hole promptly divested the star of its outer layers, speeding its evolution into a white dwarf, the dead core that remains once the star has exhausted its nuclear fuel (white dwarfs shine with residual heat, not the fusion processes of living stars).
But rather than continuing on its journey, the white dwarf was captured in orbit around the black hole, and continued to feed into it.
Based on the magnitude of the X-ray flares, and our understanding of the flares that are produced by black hole mass transfer, and the star’s orbit, King was able to constrain the mass of the star, too. He calculated that the white dwarf is around 0.21 times the mass of the Sun.
While on the lighter end of the scale, that’s a pretty standard mass for a white dwarf. And if we assume the star is a white dwarf, we can also infer – based on our understanding of other white dwarfs and stellar evolution – that the star is rich in helium, having long ago run out of hydrogen.
“It’s remarkable to think that the orbit, mass and composition of a tiny star 250 million light years away could be inferred,” King said.
Based on these parameters, he also predicted that the star’s orbit wobbles slightly, like a spinning top losing speed. This wobble should repeat every two days or so, and we may even be able to detect it, if we observe the system for long enough.
This could be one mechanism whereby black holes grow more and more massive over time. But we’ll need to study more such systems to confirm it, and they may not be easy to detect.
For one, GSN 069’s black hole is lower mass, which means that the star can travel on a closer orbit. To survive a more massive black hole, a star would have to be on a much larger orbit, which means any periodicity in the feeding would be easier to miss. And if the star were to stray too close, the black hole would destroy it.
But the fact that one has been identified offers hope that it’s not the only such system out there.
“In astronomical terms, this event is only visible to our current telescopes for a short time – about 2,000 years, so unless we were extraordinarily lucky to have caught this one, there may be many more that we are missing elsewhere in the Universe,” King said.
As for the star’s future, well, if nothing else is to change, the star will stay right where it is, orbiting the black hole, and continuing to be slowly stripped for billions of years. This will cause it to grow in size and decrease in density – white dwarfs are only a little bigger than Earth – until it’s down to a planetary mass, maybe even eventually turning into a gas giant.
“It will try hard to get away, but there is no escape,” King said. “The black hole will eat it more and more slowly, but never stop.”
The research has been published in the Monthly Notices of the Royal Astronomical Society.
A version of this article was first published in April 2020.
There are supermassive black holes. There are ultramassive black holes. How large can these strange objects grow? Well, there could be something even bigger than ultramassive: stupendously large black holes, according to the latest research.
Such hypothetical black holes – larger than 100 billion times the mass of the Sun – have been explored in a new paper which names them SLABs, an acronym that stands for “Stupendously LArge Black holeS”.
“We already know that black holes exist over a vast range of masses, with a supermassive black hole of 4 million solar masses residing at the centre of our own galaxy,” explained astronomer Bernard Carr of Queen Mary University London.
“Whilst there isn’t currently evidence for the existence of SLABs, it’s conceivable that they could exist and they might also reside outside galaxies in intergalactic space, with interesting observational consequences.”
Black holes have only a few somewhat broad mass categories. There are stellar-mass black holes; those are black holes that are around the mass of a star, up to around 100 solar masses. The next category up is intermediate mass black holes, and how large they get seems to depend on who you talk to. Some say 1,000 solar masses, some say 100,000, and others say 1 million; whatever the upper limit is, these seem to be pretty rare.
Supermassive black holes (SMBHs) are much, much larger, on the order of millions to billions of solar masses. These include the SMBH at the heart of the Milky Way, Sagittarius A*, at 4 million solar masses, and the most photogenic SMBH in the Universe, M87*, at 6.5 billion solar masses.
The chonkiest black holes we’ve detected are ultramassive, more than 10 billion (but less than 100 billion) solar masses. These include an absolute beast clocking in at 40 billion solar masses in the centre of a galaxy named Holmberg 15A.
“However, surprisingly, the idea of SLABs has largely been neglected until now,” Carr said.
“We’ve proposed options for how these SLABs might form, and hope that our work will begin to motivate discussions amongst the community.”
The thing is, scientists don’t quite know how really big black holes form and grow. One possibility is that they form in their host galaxy, then grow bigger and bigger by slurping up a whole lot of stars and gas and dust, and collisions with other black holes when galaxies merge.
This model has an upper limit of around 50 billion solar masses – that’s the limit at which the object’s prodigious mass would require an accretion disc so massive it would fragment under its own gravity. But there’s also a significant problem: Supermassive black holes have been found in the early Universe at masses too high to have grown by this relatively slow process in the time since the Big Bang.
Another possibility is something called primordial black holes, first proposed in 1966. The theory goes that the varying density of the early Universe could have produced pockets so dense, they collapsed into black holes. These would not be subject to the size constraints of black holes from collapsed stars, and could be extremely small or, well, stupendously large.
The extremely small ones, if they ever existed, would probably have evaporated due to Hawking radiation by now. But the much, much larger ones could have survived.
So, based on the primordial black hole model, the team calculated exactly how stupendously large these black holes could be, between 100 billion and 1 quintillion (that’s 18 zeroes) solar masses.
The purpose of the paper, the researchers said, was to consider the effect of such black holes on the space around them. We may not be able to see SLABs directly – black holes that aren’t accreting material are invisible, since light cannot escape their gravity – but massive invisible objects can still be detected based on the way space around them behaves.
Gravity, for instance, curves space-time, which causes the light travelling through those regions to also follow a curved path; this is called a gravitational lens, and the effect could be used to detect SLABs in intergalactic space, the team said.
The huge objects also would have implications for the detection of dark matter, the invisible mass that’s injecting way more gravity into the Universe than there should be – based on what we can actually directly detect.
One hypothetical dark matter candidate, weakly interacting massive particles (WIMPs), would accumulate in the region around a SLAB due to the immense gravity, in such concentrations that they would collide with and annihilate each other, creating a gamma-radiation halo.
And primordial black holes are themselves a dark matter candidate, too.
“SLABs themselves could not provide the dark matter,” Carr said. “But if they exist at all, it would have important implications for the early Universe and would make it plausible that lighter primordial black holes might do so.”
Also, we couldn’t resist calculating the size of a 1 quintillion solar mass black hole. The event horizon would end up over 620,000 light-years across. Uh. Stupendous.
The team’s research has been published in the Monthly Notices of the Royal Astronomical Society.
A new study describes a cloudless, Jupiter-like exoplanet.Illustration: M. Weiss/Center for Astrophysics | Harvard & Smithsonian
Nearly 600 light-years from Earth, the exoplanet known as WASP-62b whips around its host star at a breakneck pace. The planet is a hot Jupiter, and despite its gassy constitution, its atmosphere is completely cloudless, according to a study published this month in the Astrophysical Journal Letters.
WASP-62b was first detected in 2012 in a sweep by the Wide Angle Search for Planets South survey (hence the acronym in its name). The survey detects exoplanets by spotting them as they pass in front of their host stars, causing a dip in the brightness of the star’s shine.
“We can’t actually see these planets directly. It’s like looking at a firefly next to a streetlamp,” Munazza Alam, an astronomer at the Harvard-Smithsonian Center for Astrophysics and lead author of the recent paper, said in a phone call. “We’re gleaning all this information about the planet’s atmosphere from what we call combined light observations, meaning we’re looking at the light from both the star and the planet.”
Hot Jupiters are a class of exoplanets, named because they are gas giants (like our local Jupiter) that orbit close to their host stars and thus are quite hot. They stand among super-Earths, mini-Neptunes, and a slew of other classifications that seek to describe exoplanets based on their archetypes in our local solar system. As a result of a hot Jupiter’s proximity to its host star, the exoplanets have extremely short orbital periods. If WASP-62b’s orbit began on a Monday morning for Earth, its year would be over before you clocked out for the weekend.
Within the Milky Way, Alam said, hot Jupiters are rarer than smaller planets, and among exoplanets, it’s more common to find cloudy atmospheres. That makes this hot Jupiter a bit of an oddball.
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The team looked at spectroscopic data gathered by the Hubble Space Telescope that focused on quantities of potassium and sodium in the atmosphere. None of the former turned up, but sodium was detected in “whopping” amounts, Alam said, suggesting that the atmosphere of WASP-62b was clear at the pressures detected by Hubble. The results make the planet the first hot Jupiter with a cloud-free atmosphere and only the second exoplanet with such a clear atmosphere after a hot Saturn (WASP-96b) detected in 2018. Both planets have that significant sodium content, which appears in a tent-like peak in the data, that make for a cloud-free gas giant.
Down the line, the team aims to probe different atmospheric layers of the hot Jupiter that are not detectable by Hubble. Future observations of the exoplanet will be done with the upcoming James Webb Space Telescope, which will be able to see in near-infrared.
“Kepler showed us that there are thousands of planets out there, and TESS is doing that as well in different parts of the sky,” Alam said. “We found thousands of smaller planets, which is really changing the demographics of the planet population as we knew it.”
Artist illustration of WASP-62b, the first Jupiter-like planet detected without clouds or haze in its observable atmosphere. The illustration is drawn from the perspective of an observer nearby to the planet. Credit: M. Weiss/Center for Astrophysics | Harvard & Smithsonian
Astronomers at the Center for Astrophysics | Harvard & Smithsonian have detected the first Jupiter-like planet without clouds or haze in its observable atmosphere. The findings were published this month in the Astrophysical Journal Letters.
Named WASP-62b, the gas giant was first detected in 2012 through the Wide Angle Search for Planets (WASP) South survey. Its atmosphere, however, had never been closely studied until now.
“For my thesis, I have been working on exoplanet characterization,” says Munazza Alam, a graduate student at the Center for Astrophysics who led the study. “I take discovered planets and I follow up on them to characterize their atmospheres.”
Known as a “hot Jupiter,” WASP-62b is 575 light years away and about half the mass of our solar system’s Jupiter. However, unlike our Jupiter, which takes nearly 12 years to orbit the sun, WASP-62b completes a rotation around its star in just four-and-a-half days. This proximity to the star makes it extremely hot, hence the name “hot Jupiter.”
Using the Hubble Space Telescope, Alam recorded data and observations of the planet using spectroscopy, the study of electromagnetic radiation to help detect chemical elements. Alam specifically monitored WASP-62b as it swept in front of its host star three times, making visible light observations, which can detect the presence of sodium and potassium in a planet’s atmosphere.
“I’ll admit that at first I wasn’t too excited about this planet,” Alam says. “But once I started to take a look at the data, I got excited.”
While there was no evidence of potassium, sodium’s presence was strikingly clear. The team was able to view the full sodium absorption lines in their data, or its complete fingerprint. Clouds or haze in the atmosphere would obscure the complete signature of sodium, Alam explains, and astronomers usually can only make out small hints of its presence.
“This is smoking gun evidence that we are seeing a clear atmosphere,” she says.
Cloud-free planets are exceedingly rare; astronomers estimate that less than 7 percent of exoplanets have clear atmospheres, according to recent research. For example, the first and only other known exoplanet with a clear atmosphere was discovered in 2018. Named WASP-96b, it is classified as a hot Saturn.
Astronomers believe studying exoplanets with cloudless atmospheres can lead to a better understanding of how they were formed. Their rarity “suggests something else is going on or they formed in a different way than most planets,” Alam says. Clear atmospheres also make it easier to study the chemical composition of planets, which can help identify what a planet is made of.
With the launch of the James Webb Space Telescope later this year, the team hopes to have new opportunities to study and better understand WASP-62b. The telescope’s improved technologies, like higher resolution and better precision, should help them probe the atmosphere even closer to search for the presence of more elements, such as silicon.
Astronomers see unexpected molecule in exoplanet atmosphere
More information:
Munazza K. Alam et al, Evidence of a Clear Atmosphere for WASP-62b: The Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone, The Astrophysical Journal (2021). DOI: 10.3847/2041-8213/abd18e
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Astronomers discover first cloudless, Jupiter-like planet (2021, January 22)
retrieved 22 January 2021
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