Astronomy

Season Two of MGM+'s sci-fi mystery show is back with new characters and more cosmic conflict on April 7.

In the buildup to the April 8 total solar eclipse, researchers set about discovering how often cities experience eclipses and where, if anywhere, on Earth witnesses the most of these events.

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In late 2021 there was a total solar eclipse visible only at the end of the Earth.

When light strikes the atmosphere all sorts of interesting things can happen. Water vapor can split sunlight into a rainbow arc of colors, corpuscular rays can stream through gaps in clouds like the light from heaven, and halos and sundogs can appear due to sunlight reflecting off ice crystals. And then there is the glory effect, which can create a colorful almost saint-like halo around objects.

Like rainbows, glories are seen when facing away from the light source. They are often confused with circular rainbows because of their similarity, but glories are a unique effect. Rainbows are caused by the refraction of light through water droplets, while glories are caused by the wave interference of light. Because of this, a glory is most apparent when the water droplets of a cloud or fog are small and uniform in size. The appearance of a glory gives us information about the atmosphere. We have assumed that some distant exoplanets would experience glories similar to Earth, but now astronomers have found the first evidence of them.

A solar glory seen from an airplane. Credit: Brocken Inaglory

The observations come from the Characterising ExOplanet Satellite (Cheops) as well as observations from other observatories of an exoplanet known as WASP-76b. It’s not the kind of exoplanet where you’d expect a glory to appear. WASP-76b is not a temperate Earth-like world with a humid atmosphere, but a hellish hot Jupiter with a surface temperature of about 2,500 Kelvin. Because of this, the team wasn’t looking for extraterrestrial glories but rather studying the odd asymmetry of the planet’s atmosphere.

WASP-76b orbits its star at a tenth of the distance of Mercury from the Sun. At such a close distance the world is likely tidally locked, with one side forever boiling under its sun’s heat and the other side always in shadow. No such planet exists in our solar system, so astronomers are eager to study how this would affect the atmosphere of such a world. Previous studies have shown that the atmosphere is not symmetrical. The star-facing side is puffed up by the immense heat, while the atmosphere of the dark side is more dense.

For three years the team observed WASP-76b as it passed in front of and behind its star, capturing data on the intersection between the light and dark side. They found that on the planet’s eastern terminator (the boundary between light and dark sides) there was a surprising increase in light. This extra glow could be caused by a glory effect. It will take more observations to confirm this effect but if verified it will be the first glory observed beyond our solar system. Currently, glories have only been observed on Earth and Venus.

The presence of a glory on WASP-76b would mean that spherical droplets must have been present in the atmosphere for at least three years. This means either they are stable within the atmosphere, or they are constantly replenished. One possibility is that the glory is caused by iron droplets that rain from the sky on the cooler side of the planet. Even if this particular effect is not confirmed, the ability of modern telescopes to capture this data suggests that we will soon be able to study many subtle effects of exoplanet atmospheres.

Reference: Demangeon, O. D. S., et al. “Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b.” Astronomy & Astrophysics 684 (2024): A27.

The post The First Atmospheric Rainbow on an Exoplanet? appeared first on Universe Today.

Astronomers routinely provide the ages of the stars they study. But the methods of measuring ages aren’t 100% accurate. Measuring the ages of distant stars is a difficult task.

The Nancy Grace Roman Space Telescope should make some progress.

Stars like our Sun settle into their main sequence lives of fusion and change very little for billions of years. It’s like watching middle-aged adults go about their business during their working lives. They get up, drive to work, sit at a desk, then drive home.

But what can change over time is their rotation rate. The Sun now rotates about once a month. When it was first formed, it rotated more rapidly.

But over time, the Sun’s rotation rate, and the rotation rate of stars the same mass or lower than the Sun’s, will slow down. The slowdown is caused by interactions between the star’s magnetic fields and the stellar wind, the stream of high-energy protons and electrons emitted by stars. Over time, these interactions reduce a star’s angular momentum, and its rotation slows. The phenomenon is called “magnetic braking,” and it depends on the strength of a star’s magnetic fields.

When the Sun rotates, the magnetic field lines rotate with it. The combination is almost like a solid object. Ionized material from the solar wind will be carried along the field lines and, at some point, will escape the magnetic field lines altogether. That reduces the Sun’s angular momentum. Image Credit: By Coronal_Hole_Magnetic_Field_Lines.svg: Sebman81Sun_in_X-Ray.png: NASA Goddard Laboratory for AtmospheresCelestia_sun.jpg: NikoLangderivative work: Aza (talk) – Coronal_Hole_Magnetic_Field_Lines.svgSun_in_X-Ray.pngCelestia_sun.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8258519

The more rapidly a star initially spins, the stronger its magnetic fields. That means they slow down faster. After about one billion years of life, stars of the same age and mass will spin at the same rate. Once astronomers know a star’s mass and rotation rate, they can estimate its age. Knowing stars’ ages is critical in research. It makes everything astronomers do more accurate, including piecing together the Milky Way’s history.

The problem is that measuring rotation rates is challenging. One method is to observe spots on stars’ surfaces and watch as they come into and out of view. All stars have star spots, though their characteristics vary quite a bit. In fact, stars can have dozens of spots, and the spots change locations. Therein lies the difficulty. It’s extremely difficult to figure out the periodicity when dozens of spots change locations on the star’s surface.

This is where the Nancy Grace Roman Space Telescope (the Roman) comes in. It’s scheduled for launch in May 2027 to begin its five-year mission. It’s a wide-field infrared survey telescope with multiple science objectives. One of its main programs is the Galactic Bulge Time Domain Survey. That effort will gather detailed information on hundreds of millions of stars in the Milky Way’s galactic bulge.

This is a simulated image of what the Roman Space Telescope will see when it surveys the Milky Way’s galactic bulge. The telescope will observe hundreds of millions of stars in the region. Image Credit: Matthew Penny (Louisiana State University)

The Roman will generate an enormous amount of data. Much of it will be measurements of how the brightness of hundreds of thousands of stars changes. But untangling those measurements and figuring out what those changes in brightness mean for stellar rotation requires help from AI.

Astronomers at the University of Florida are developing AI to extract stellar rotation periods from all that data.

Zachary Claytor is a postdoc at the University of Florida and the AI project’s science principal investigator. Their AI is called a convolutional neural network. This type of AI is well-suited to analyzing images and is used in image classification and medical image analysis, among other things.

AI needs to be trained before it can do its job. In this case, Claytor and his associates wrote a computer program to generate simulated stellar light curves for the AI to process and learn from.

“This program lets the user set a number of variables, like the star’s rotation rate, the number of spots, and spot lifetimes. Then it will calculate how spots emerge, evolve, and decay as the star rotates and convert that spot evolution to a light curve – what we would measure from a distance,” explained Claytor.

Claytor and his co-researchers have already tested their AI on data from NASA’s TESS, the Transiting Exoplanet Survey Satellite. The longer a star’s rotation period is, the more difficult it is to measure. But the team’s AI demonstrated that it could successfully determine these periods in TESS data.

The Roman’s Galactic Bulge Time Domain Survey is still being designed. So astronomers can use this AI-based effort to help design the survey.

“We can test which things matter and what we can pull out of the Roman data depending on different survey strategies. So when we actually get the data, we’ll already have a plan,” said Jamie Tayar, assistant professor of astronomy at the University of Florida and the program’s principal investigator.

“We have a lot of the tools already, and we think they can be adapted to Roman,” she added.

Artist’s impression of the Nancy Grace Roman Space Telescope, named after NASA’s first Chief of Astronomy. When launched later this decade, the telescope will measure the rotational periods of hundreds of thousands of stars and, with the help of AI, will determine their ages. Credits: NASA

Measuring stellar ages is difficult, yet age is a key factor in understanding any star. Astronomers use various methods to measure ages, including evolutionary models, a star’s membership in a cluster of similarly-aged stars, and even the presence of a protoplanetary disk. But no single method can measure every star’s age, and each method has its own drawbacks.

If the Roman can break through this barrier and accurately measure stellar rotation rates, astronomers should have a leg-up in understanding stellar ages. But there’s still one problem: magnetic braking.

This method relies on a solid understanding of how magnetic braking works over time. But astronomers may not understand it as thoroughly as they’d like. For instance, research from 2016 showed that magnetic braking might not slow down older stars as much as thought. That research found unexpectedly rapid rotation rates in stars more evolved than our Sun.

Somehow, astronomers will figure this all out. The Roman Space Telescope should help, as its vast trove of data is bound to lead to some unexpected conclusions. One way or another, with the help of the Roman Space Telescope, the ESA’s Gaia mission, and others, astronomers will untangle the problem of measuring everything about stars, including their ages.

The post Roman Will Learn the Ages of Hundreds of Thousands of Stars appeared first on Universe Today.

The first total solar eclipse I saw in 2017 was a work event. For the 2024 total solar eclipse, I'm bringing my kid.

On Episode 105 of This Week In Space, Rod and Tariq talk with astronomer and meteorologist Joe Rao about the solar eclipse of 2024.

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A Russian Soyuz spacecraft carrying three people, including the first female Belarusian in space, landed in Kazakhstan early this morning (April 6).

Since it began operations in July 2022, the James Webb Space Telescope (JWST) has fulfilled many scientific objectives. In addition to probing the depths of the Universe in search of galaxies that formed shortly after the Big Bang, it has also provided the clearest and most detailed images of nearby galaxies. In the process, Webb has provided new insight into the processes through which galaxies form and evolve over billions of years. This includes galaxies like Messier 82 (M82), a “starburst galaxy” located about 12 million light-years away in the constellation Ursa Major.

Also known as the “Cigar Galaxy” because of its distinctive shape, M82 is a rather compact galaxy with a very high star formation rate. Roughly five times that of the Milky Way, this is why the core region of M82 is over 100 times as bright as the Milky Way’s. Combined with the gas and dust that naturally obscures visible light, this makes examining M82’s core region difficult. Using the extreme sensitivity of Webb‘s Near-Infrared Camera (NIRCam), a team led by the University of Maryland observed the central region of this starburst galaxy to examine the physical conditions that give rise to new stars.

The team was led by Alberto Bollato, an astronomy professor at the University of Maryland and a researcher with the Joint Space-Science Institute (JSSI). He was joined by researchers from NASA’s Jet Propulsion Laboratory, NASA Ames, the European Space Agency (ESA), the Space Telescope Science Institute (STScI), the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), the Max-Planck-Institut für Astronomie (MPIA), National Radio Astronomy Observatory (NRAO), the Infrared Processing and Analysis Center (IPAC-Caltech) and multiple universities, institutes, and observatories. Their findings are described in a paper accepted for publication in The Astrophysical Journal.

Annotated image of the starburst galaxy Messier 82 captured by Hubble (left) and Webb’s NIRCam (right). Credit: NASA/ESA/CSA/STScI/Alberto Bolatto (UMD)

Their observations were part of a Cycle 1 General Observations (GO) project – for which Bollato is the Principal Investigator (PI) – that used NIRCam data to examine the “prototypical starbursts” NGC 253 and M82 and their “cool” galactic winds. Such galaxies remain a source of fascination for astronomers because of what they can reveal about the birth of new stars in the early Universe. Starbursts are galaxies that experience rapid and efficient star formation, a phase that most galaxies went through during the early history of the Universe (ca. 10 billion years ago). Studying early galaxies in this phase is challenging due to the distances involved.

Fortunately, starburst galaxies like NGC 253 and M82 are relatively close to the Milky Way. While these galaxies have been observed before, Webb’s extreme sensitivity in the near-infrared spectrum provided the most detailed look to date. Moreover, the NIRCam observations were made using an instrument mode that prevented the galaxy’s intense brightness from overwhelming the instrument. The resulting images revealed details that have been historically obscured, such as dark brown tendrils of heavy dust that contained concentrations of iron (visible in the image as green specks).

These consist largely of supernova remnants, while small patches of red are clouds of molecular hydrogen lit up by young stars nearby. Said Rebecca Levy, second author of the study at the University of Arizona in Tucson, in a NASA press release, “This image shows the power of Webb. Every single white dot in this image is either a star or a star cluster. We can start to distinguish all of these tiny point sources, which enables us to acquire an accurate count of all the star clusters in this galaxy.”

Another key detail captured in the images is the “galactic wind” rushing out from the core, which was visible at longer infrared wavelengths. This wind is caused by the rapid rate of star formation and subsequent supernovae and has a significant influence on the surrounding environment. Studying this wind was a major objective of the project (GO 1701), which aimed to investigate how these winds interact with cold and hot material. By a central region of M82, the team was able to examine where the wind originates and the impact it has on surrounding material.

The Cigar Galaxy (M82), a starburst galaxy with high star production. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

The team was surprised by the way Webb’s NIRCam was able to trace the structure of the galactic wind via emission spectra from very small dust grains known as polycyclic aromatic hydrocarbons (PAHs) – a chemical produced when coal, wood, gasoline, and tobacco are burned. These emissions highlighted the galactic wind’s fine structure, which appeared as red filaments flowing from above and below the galaxy’s disk. Another surprise was the structure of the PAH emission, which was similar to that of the hot ionized gas in the wind. As Bollato explained:

“M82 has garnered a variety of observations over the years because it can be considered as the prototypical starburst galaxy. Both NASA’s Spitzer and Hubble space telescopes have observed this target. With Webb’s size and resolution, we can look at this star-forming galaxy and see all of this beautiful, new detail. It was unexpected to see the PAH emission resemble ionized gas. PAHs are not supposed to live very long when exposed to such a strong radiation field, so perhaps they are being replenished all the time. It challenges our theories and shows us that further investigation is required.”

The team hopes to further investigate the questions these findings raise using Webb data, which will include spectroscopic observations made using the Near-infrared Spectrograph (NIRSpec) and large-scale images of the galaxy and wind. This data will help astronomers obtain accurate ages for the star clusters and determine how long each phase of star formation lasts in starburst galaxies. As always, this information could shed light on how similar phases took place in the early Universe, helping shape galaxies like ours. As Bollato summarized:

“Webb’s observation of M82, a target closer to us, is a reminder that the telescope excels at studying galaxies at all distances. In addition to looking at young, high-redshift galaxies, we can look at targets closer to home to gather insight into the processes that are happening here – events that also occurred in the early universe.”

Further Reading: Webb Space Telescope, MPIA

The post Webb Sees a Galaxy Awash in Star Formation appeared first on Universe Today.