It's a Planet: New Evidence of Baby Planet in the Making

Artist's illustration of a small Saturn-like planet discovered in the system LkCa 15. The planet resides within dense rings of dust and gas that surround a bright yellow star. Material accumulates in a clump and arc-shape, about 60 degrees away from the planet. Note: This illustration is not to scale. Credit: M.Weiss/Center for Astrophysics | Harvard & Smithsonian

 

Astronomers have developed a new technique to identify small planets hidden in protoplanetary disks.

Cambridge, MA – Astronomers agree that planets are born in protoplanetary disks — rings of dust and gas that surround young, newborn stars. While hundreds of these disks have been spotted throughout the universe, observations of actual planetary birth and formation have proved difficult within these environments.

Now, astronomers at the Center for Astrophysics | Harvard & Smithsonian have developed a new way to detect these elusive newborn planets — and with it, "smoking gun" evidence of a small Neptune or Saturn-like planet lurking in a disk. The results are described today in The Astrophysical Journal Letters.

"Directly detecting young planets is very challenging and has so far only been successful in one or two cases," says Feng Long, a postdoctoral fellow at the Center for Astrophysics who led the new study. "The planets are always too faint for us to see because they’re embedded in thick layers of gas and dust."

Scientists instead must hunt for clues to infer a planet is developing beneath the dust.

"In the past few years, we've seen many structures pop up on disks that we think are caused by a planet's presence, but it could be caused by something else, too" Long says. "We need new techniques to look at and support that a planet is there."

For her study, Long decided to re-examine a protoplanetary disk known as LkCa 15. Located 518 light years away, the disk sits in the Taurus constellation on the sky. Scientists previously reported evidence for planet formation in the disk using observations with the ALMA Observatory.

Long dove into new high-resolution ALMA data on LkCa 15, obtained primarily in 2019, and discovered two faint features that had not previously been detected.

About 42 astronomical units out from the star — or 42 times the distance Earth is from the Sun — Long discovered a dusty ring with two separate and bright bunches of material orbiting within it. The material took the shape of a small clump and a larger arc, and were separated by 120 degrees.

Long examined the scenario with computer models to figure out what was causing the buildup of material and learned that their size and locations matched the model for the presence of a planet.

"This arc and clump are separated by about 120 degrees," she says. "That degree of separation doesn’t just happen — it’s important mathematically."

Long points to positions in space known as Lagrange points, where two bodies in motion — such as a star and orbiting planet — produce enhanced regions of attraction around them where matter may accumulate.

"We're seeing that this material is not just floating around freely, it's stable and has a preference where it wants to be located based on physics and the objects involved," Long explains.

In this case, the arc and clump of material Long detected are located at the L4 and L5 Lagrange points. Hidden 60 degrees between them is a small planet causing the accumulation of dust at points L4 and L5.

The results show the planet is roughly the size of Neptune or Saturn, and around one to three million years old. (That's relatively young when it comes to planets.)

Directly imaging the small, newborn planet may not be possible any time soon due to technology constraints, but Long believes further ALMA observations of LkCa 15 can provide additional evidence supporting her planetary discovery.

She also hopes her new approach for detecting planets — with material preferentially accumulating at Lagrange points — will be utilized in the future by astronomers.

"I do hope this method can be widely adopted in the future," she says. "The only caveat is that this requires very deep data as the signal is weak."

Long recently completed her postdoctoral fellowship at the Center for Astrophysics and will join the University of Arizona as a NASA Hubble Fellow this September.

Co-authors on the study are Sean Andrews, Chunhua Qi, David Wilner and Karin Oberg of the CfA; Shangjia Zhang and Zhaohuan Zhu of the University of Nevada; Myriam Benisty of the University of Grenoble; Stefano Facchini of the University of Milan; Andrea Isella of Rice University; Jaehan Bae of the University of Florida; Jane Huang of the University of Michigan and Ryan Loomis of the National Radio Astronomy Observatory.

This study involved high resolution ALMA observations taken with Band 6 (1.3mm) and Band 7 (0.88mm) receivers.

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About the Center for Astrophysics | Harvard & Smithsonian

The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask—and ultimately answer—humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.

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Source: Harvard-Smithsonian Center for Astrophysics (CfA)

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Beginnings of a Branch

The Sagittarius stellar stream wrapping around the Milky Way
Credit: David Law, UCLA

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Editor’s note: Ben Casseseis a second-year graduate student at Columbia University, and he was recently selected as the 2022–2023AAS Media Fellow. We’re excited to welcome Ben to the team and look forward to featuring his writing on AAS Nova regularly!

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The Sagittarius stellar stream is split into two branches: a large, bright river of stars and a smaller, fainter parallel creek. What’s the cause of this fissure, and where did the stars in this sibling stream come from?

The on-sky locations for a sample of actual stars in the Sgr stream, overplotted with the final locations of the test particles in their simulation that ended in the faint branch. Credit: Oria et al. 2022

A Stream of Stripped Stars

The Sagittarius (Sgr) dwarf galaxy has a complicated past with the Milky Way. The two galaxies have been slowly merging for several billion years, but the process has not gone smoothly for both parties. Although the Milky Way has been largely unaffected, many of Sgr’s original constituent stars have been stripped away and stretched into a long filament that wraps all the way around our sky. This is referred to as the Sagittarius stellar stream, and it was first discovered in the early 2000s. 

For more than two decades now, astronomers have attempted to recreate the original conditions of this destructive embrace and envision what this contorted stream once looked like. Several models can reproduce the basic structure of the remains we see today, but the models that recreate the separation between bright and faint branches also make incorrect predictions about the spin of Sgr’s core. Now, a team led by Pierre-Antoine Oria (University of Strasbourg) has proposed a new origin for this faint branch that better matches our observations.

The locations of selected test particles over the course of a simulation. Note the difference in scales between the top left panel and all other panels: this initial zoom shows that all particles that ended in the faint branch began nestled in initial spirals. Click to enlarge. Credit: Oria et al. 2022

 Disky Beginnings

To reach their conclusion, Oria and collaborators created a suite of artificial disks, each with their own inclination, angular momentum, and collection of massless test particles meant to represent stars. They then injected these disks into a previous model of the Sgr–Milky Way merger that did not reproduce the separation into different branches. After letting the simulation run, they checked which disk configuration best recreated the faint stream. Curiously, this best disk turned out to be nearly perpendicular to both the Milky Way’s plane and Sgr’s orbital plane.

After establishing that the faint branch stars likely came from this rotated disk, the team went a step further and determined not just the orientation of the parent disk but also the structure within it. By flagging particles that ended up in the faint branch at the end of the simulation, the team rewound the clock to check where those particles had begun their simulated lives. Although the authors had distributed the stars randomly throughout the initial disk without regard for any pattern, it turned out that all the stars that would someday arrive in the faint branch initially traced out a spiral structure.

New Ingredients

In summary, Oria and collaborators suggest that the stars that make up the faint branch of the Sgr stellar stream likely originated in a misaligned, spiraled disk. This model successfully reproduces today’s observed faint branch structure, but it is not without flaws: it over-predicts the thickness of the main branch and opens new questions about the origins of the spiral. Excitingly, though, the authors suggest that their disk can be added to a more complete model of the Sgr merger in the future, meaning this new ingredient brings us one step closer to a full reconstruction of Sgr and its slow destruction.

Citation

Revisiting a Disky Origin for the Faint Branch of the Sagittarius Stellar Stream,” Pierre-Antoine Oria et al 2022 932 doi:10.3847/2041-8213/ac738c

By Ben Cassese

Source: American Astronomical Society - AAS Nova

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Featured Image: Ice in the Shadow of Mercury’s Craters

New models of various properties of Prokofiev crater on Mercury: (a) elevation, (b) illumination, (c) maximum temperature, and (d) depth at which ice is stable. These maps have a resolution of 125 meters per pixel. Click for high-resolution version. Credit: Barker et al. 2022

With daytime temperatures soaring to 427℃ (800℉), Mercury seems like an unlikely place to find ice, but the poles of the airless planet can be surprisingly frosty. Using images and elevation data from the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft, a team led by Michael Barker (NASA’s Goddard Space Flight Center) inspected a permanently shadowed north polar crater named Prokofiev, which contains a radar-bright region thought to be surface ice. As shown in the images to the right, Barker and collaborators modeled the crater’s elevation, illumination, maximum temperature, and depth below the surface at which water ice could be stable. This modeling confirmed that the crater has the right conditions to host surface ice, and further analysis suggests that the radar-bright region may be a layer of ice up to 26 meters thick. The ice isn’t pure water, though — part of the ice is covered by a dark silicate or hydrocarbon material, the exact nature of which is unknown. To learn more about this icy investigation, be sure to check out the full article below!

Citation

“New Constraints on the Volatile Deposit in Mercury’s North Polar Crater, Prokofiev,” Michael K. Barker et al 2022 Planet. Sci. J. 3 188. doi:10.3847/PSJ/ac7d5a

By Kerry Hensley

Source: American Astronomical Society - AAS Nova

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SNR 0519-69.0: Setting the Clock on a Stellar Explosion

SNR 0519-69.0
Credit: X-ray: NASA/CXC/GSFC/B. J. Williams et al.; Optical: NASA/ESA/STScI

JPEG (431.1 kb)-Large JPEG (3.1 MB)-Tiff (8.7 MB)-More Images

A Tour of SNR 0519-69.0 - More Animations

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While astronomers have seen the debris from scores of exploded stars in the Milky Way and nearby galaxies, it is often difficult to determine the timeline of the star’s demise. By studying the spectacular remains of a supernova in a neighboring galaxy using NASA telescopes, a team of astronomers has found enough clues to help wind back the clock.

The supernova remnant called SNR 0519-69.0 (SNR 0519 for short) is the debris from an explosion of a white dwarf star. After reaching a critical mass, either by pulling matter from a companion star or merging with another white dwarf, the star underwent a thermonuclear explosion and was destroyed. Scientists use this type of supernova, called a Type Ia, for a wide range of scientific studies ranging from studies of thermonuclear explosions to measuring distances to galaxies across billions of light-years.

SNR 0519 is located in the Large Magellanic Cloud, a small galaxy 160,000 light-years from Earth. This composite image shows X-ray data from NASA’s Chandra X-ray Observatory and optical data from NASA’s Hubble Space Telescope. X-rays from SNR 0519 with low, medium and high energies are shown in green, blue, and purple respectively, with some of these colors overlapping to appear white. Optical data shows the perimeter of the remnant in red and stars around the remnant in white.

Astronomers combined the data from Chandra and Hubble with data from NASA’s retired Spitzer Space telescope to determine how long ago the star in SNR 0519 exploded and learn about the environment the supernova occurred in. This data provides scientists a chance to “rewind” the movie of the stellar evolution that has played out since and figure out when it got started.

The researchers compared Hubble images from 2010, 2011, and 2020 to measure the speeds of material in the blast wave from the explosion, which range from about 3.8 million to 5.5 million miles (9 million kilometers) per hour. If the speed was toward the upper end of those estimated speeds, the astronomers determined that light from the explosion would have reached Earth about 670 years ago, or during the Hundred Years’ War between England and France and the height of the Ming dynasty in China.

However, it’s likely that the material has slowed down since the initial explosion and that the explosion happened more recently than 670 years ago. The Chandra and Spitzer data provide clues that this is the case. Astronomers found the brightest regions in X-rays of the remnant are where the slowest-moving material is located, and no X-ray emission is associated with the fastest-moving material.

These results imply that some of the blast wave has crashed into dense gas around the remnant, causing it to slow down as it traveled. Astronomers may use additional observations with Hubble to determine more precisely when the time of the star’s demise should truly be set.

A paper describing these results was published in the August issue of The Astrophysical Journal, and a preprint is available here. The authors of the paper are Brian Williams (NASA’s Goddard Space Flight Center (GSFC) in Greenbelt, Maryland); Parviz Ghavamian (Towson University, Towson, Maryland); Ivo Seitenzahl (University of New South Wales, Australian Defence Force Academy, Canberra, Australia); Stephen Reynolds (North Carolina State University (NCSU), Raleigh, NC); Kazimierz Borkowski (North Carolina State University, Raleigh, NC) and Robert Petre (GSFC). NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Quick Look: Setting the Clock on a Stellar Explosion

Source: NASA’s Chandra X-ray Observatory

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NASA's Hubble Finds Spiraling Stars, Providing Window into Early Universe

Spatial Distribution of NGC 346 Stars

The massive star cluster NGC 346, located in the Small Magellanic Cloud, has long intrigued astronomers with its unusual shape. Now researchers using two separate methods have determined that this shape is partly due to stars and gas spiraling into the center of this cluster in a river-like motion. The red spiral superimposed on NGC 346 traces the movement of stars and gas toward the center. Scientists say this spiraling motion is the most efficient way to feed star formation from the outside toward the center of the cluster. Credits: Illustration: NASA, ESA, Andi James (STScI). Release images

Nature likes spirals — from the whirlpool of a hurricane, to pinwheel-shaped protoplanetary disks around newborn stars, to the vast realms of spiral galaxies across our universe.

Now astronomers are bemused to find young stars that are spiraling into the center of a massive cluster of stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way.

The outer arm of the spiral in this huge, oddly shaped stellar nursery called NGC 346 may be feeding star formation in a river-like motion of gas and stars. This is an efficient way to fuel star birth, researchers say.

The Small Magellanic Cloud has a simpler chemical composition than the Milky Way, making it similar to the galaxies found in the younger universe, when heavier elements were more scarce. Because of this, the stars in the Small Magellanic Cloud burn hotter and so run out of their fuel faster than in our Milky Way.

Though a proxy for the early universe, at 200,000 light-years away the Small Magellanic Cloud is also one of our closest galactic neighbors.

Learning how stars form in the Small Magellanic Cloud offers a new twist on how a firestorm of star birth may have occurred early in the universe's history, when it was undergoing a "baby boom" about 2 to 3 billion years after the big bang (the universe is now 13.8 billion years old).

The new results find that the process of star formation there is similar to that in our own Milky Way.

Only 150 light-years in diameter, NGC 346 boasts the mass of 50,000 Suns. Its intriguing shape and rapid star-formation rate has puzzled astronomers. It took the combined power of NASA's Hubble Space Telescope and the European Southern Observatory's Very Large Telescope (VLT) to unravel the behavior of this mysterious-looking stellar nesting ground.

"Stars are the machines that sculpt the universe. We would not have life without stars, and yet we don't fully understand how they form," explained study leader Elena Sabbi of the Space Telescope Science Institute in Baltimore. "We have several models that make predictions, and some of these predictions are contradictory. We want to determine what is regulating the process of star formation, because these are the laws that we need to also understand what we see in the early universe."

Researchers determined the motion of the stars in NGC 346 in two different ways. Using Hubble, Sabbi and her team measured the changes of the stars' positions over 11 years. The stars in this region are moving at an average velocity of 2,000 miles per hour, which means that in 11 years they move 200 million miles. This is about 2 times the distance between the Sun and the Earth.

But this cluster is relatively far away, inside a neighboring galaxy. This means the amount of observed motion is very small and therefore difficult to measure. These extraordinarily precise observations were possible only because of Hubble's exquisite resolution and high sensitivity. Also, Hubble's three-decade-long history of observations provides a baseline for astronomers to follow minute celestial motions over time.

The second team, led by Peter Zeidler of AURA/STScI for the European Space Agency, used the ground-based VLT's Multi Unit Spectroscopic Explorer (MUSE) instrument to measure radial velocity, which determines whether an object is approaching or receding from an observer.

"What was really amazing is that we used two completely different methods with different facilities and basically came to the same conclusion, independent of each other," said Zeidler. "With Hubble, you can see the stars, but with MUSE we can also see the gas motion in the third dimension, and it confirms the theory that everything is spiraling inwards."

But why a spiral?

"A spiral is really the good, natural way to feed star formation from the outside toward the center of the cluster," explained Zeidler. "It's the most efficient way that stars and gas fueling more star formation can move towards the center."

Half of the Hubble data for this study of NGC 346 is archival. The first observations were taken 11 years ago. They were recently repeated to trace the motion of the stars over time. Given the telescope's longevity, the Hubble data archive now contains more than 32 years of astronomical data powering unprecedented, long-term studies.

"The Hubble archive is really a gold mine," said Sabbi. "There are so many interesting star-forming regions that Hubble has observed over the years. Given that Hubble is performing so well, we can actually repeat these observations. This can really advance our understanding of star formation."

The teams'findings appear Sept. 8 in The Astrophysical Journal.

Observations with NASA's James Webb Space Telescope should be able to resolve lower-mass stars in the cluster, giving a more holistic view of the region. Over Webb's lifespan, astronomers will be able to repeat this experiment and measure the motion of the low-mass stars. They could then compare the high-mass stars and the low-mass stars to finally learn the full extent of the dynamics of this nursery.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

Source: HubbleSite/News

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Space Telescope Science Institute, Baltimore, Maryland

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AURA/STScI for the European Space Agency

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Related Links and Documents:

• Science Paper: The science paper by E. Sabbi et al., PDF (2.24 MB)
• Science Paper: The science paper by P. Zeidler et al., PDF (35.28 MB)
• NASA's Hubble Portal
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Discovery of Two Temperate Super-Earths, the Outer One Orbits in the Habitable Zone

Figure 1: A conceptual rendering of the discovery
Credit: Astrobiology Center/MuSCAT team

Astronomers have announced the discovery of two temperate "super-Earth" planets orbiting a small cool star LP 890-9 (also called TOI-4306 or SPECULOOS-2) located about 100 light-years away from Earth. The outer planet, called LP 890-9 c, orbits in the so-called "habitable zone" where the planetary surface is potentially capable of maintaining liquid water. This discovery was made possible by international collaboration between the SPECULOOS team led by researchers at the University of Liège, a Japanese TESS follow-up team from the University of Tokyo and Astrobiology Center, and worldwide researchers participating in the TESS Follow-up Observing Program.

NASA's Transiting Exoplanet Survey Satellite (TESS) is currently monitoring the sky to search for exoplanets by the transit method which finds periodic dimming of stars due to planets transiting in front of the stars. TESS found a periodic dimming of LP 890-9 every 2.73 days and announced it as a transiting planet candidate TOI-4306.01 in July 2021.

Worldwide astronomers participating in the TESS Follow-up Observing Program (TFOP) started follow-up observations of TOI-4306.01 from August 2021 to confirm the planetary nature of TOI-4306.01. Such follow-up observations are required because similar periodic dimming can be caused by eclipsing binary stars.

The Japanese TESS follow-up team led by Norio Narita at the University of Tokyo and Astrobiology Center observed LP 890-9 with the 4-color simultaneous camera MuSCAT3 installed on the Las Cumbres Observatory 2 m Faulkes Telescope North at the Haleakala Observatory, Maui and the InfraRed Doppler instrument (IRD) installed on the Subaru Telescope on Maunakea, Hawai`i Island, and confirmed the planetary nature of TOI-4306.01 by October 2021.

On the other hand, the SPECULOOS team conducted follow-up observations not only for transits of TOI-4306.01 but also for continuous monitoring of LP 890-9 to search for possible additional transiting planets in the system that may have been missed by TESS. The observations by the SPECULOOS team not only confirmed the first planet, but also allowed the detection of transits of a second, previously unknown planet in October and November 2021.

Because the data from the SPECULOOS team alone could not narrow down the orbital period of the second planet candidate, the MuSCAT team collaborated with the SPECULOOS team to follow-up on the second candidate with MuSCAT3 and finally determined the orbital period to be about 8.46 days in January 2022.

"Radial velocity measurements of LP 890-9 with IRD on the Subaru Telescope put stringent constraints on the masses of orbiting bodies, proving the planetary nature of the 2 transiting bodies orbiting around LP 890-9," explains Norio Narita, a professor at the University of Tokyo and the principal investigator of the MuSCAT team.

Once confirmed as actual planets, the 2 planets earned the official designation LP 890-9 b and LP 890-9 c. The two super-Earths, LP 890-9 b and LP 890-9 c, have radii of 1.32 Earth radii and 1.37 Earth radii, respectively. Planets with such radii are theoretically thought to be big, rocky planets. The outer planet LP 890-9 c orbits in the habitable zone of the host star. This is because the host star LP 890-9 is smaller (about 15% of the radius of the Sun) and cooler (about 2,600 degrees Celsius) than the Sun (about 5,500 degrees Celsius).

Figure 2: A picture of IRD, which was installed on the Subaru Telescope in 2018 and thereafter has been producing excellent results for exploring exoplanets around cool stars. In this study, IRD constrained the masses of two transiting planets LP 890-9 b and LP 890-9 c to be less than 13.2 Earth masses and 25.3 Earth masses, respectively. (Credit: Astrobiology Center)

Figure 3: A picture of MuSCAT3, assembled at the University of Tokyo in August 2020. MuSCAT3 was installed on the Las Cumbres Observatory 2 m Faulkes Telescope North at the Haleakala Observatory, Maui. (Credit: MuSCAT team)

The next step in studies of LP 890-9 c would be atmospheric characterization. The transiting configuration of the planet allows us to investigate light from the host star which passes through the planetary atmosphere during transits. Such follow-up observations will provide insight on atmospheric compositions and the presence/absence of clouds/haze in the atmosphere. Future studies of the atmospheres of rocky planets in the habitable zone will be important to understand Earth's place in the Universe. In this respect, the current discovery provides a prime target for further study.

These findings were published online in the journal Astronomy & Astrophysics on September 7, 2022 (Delrez et al. "Two temperate super-Earths transiting a nearby late-type M dwarf").

Source: Subaru Telescope

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Simulations Suggest Magnetic Fields Made the First Stars Form Solo

An artist's impression of the first stars in the universe going supernova.
Credit: NAOJ

The first stars in the universe, known as Population III stars, formed just a few hundred million years after the Big Bang. While researchers expect that most Population III stars led bright, brief lives, those with masses less than 0.8 solar mass would still be shining faintly today. Can magnetic fields in the early universe explain why we’ve yet to find these stars?

An infrared image of the Orion star-forming region with magnetic field lines measured by the Stratospheric Observatory for Infrared Astronomy traced on top. Credit: NASA/SOFIA/D. Chuss, et al., and European Southern Observatory/M.McCaughrean, et al

Producing Population III Stars

There are many possible explanations for why low-mass Population III stars are so elusive, but the simplest explanation might be that they never existed at all. It’s challenging to prove that something doesn’t exist in the universe, but simulations give us a way to explore whether low-mass Population III stars could have formed in the conditions that existed when the first stars were born.

Previous research suggests that the early universe was suffused with a subtle magnetic field that was about a trillion times weaker than the fields measured in typical star-forming regions in the universe today. Magnetic fields play an important role in shaping — and sometimes suppressing — star formation in the local universe, leading researchers to wonder if the weak magnetic fields in the early universe could have halted the formation of low-mass stars entirely.

Simulation results for the unmagnetized case (top row) and the case in which the magnetic field strength was 10-20 Gauss (middle and bottom row). The top and middle rows show how the density of the gas varied between the two simulations at 0, 10, and 1,000 years of simulation time. The bottom row shows how the magnetic field strength was amplified and evolved over time in the magnetized case. Click for high-resolution version. Credit: Hirano & Machida 2022

Magnetic Magnification

Shingo Hirano (University of Tokyo and Kyushu University, Japan) and Masahiro Machida (Kyushu University, Japan) modeled the collapse of a cloud of gas under the conditions present in the early universe to understand how magnetic fields might have influenced the formation of the first stars.

The team performed magnetohydrodynamic simulations of a gas cloud with weak initial magnetic field strengths of 0, 10-20, 10-15, and 10-10 Gauss. In the unmagnetized case, the cloud fragmented into a massive (~200 solar masses) central protostar and a handful of smaller protostars, all of which persisted until the end of the simulation at 1,000 years.

In the magnetized cases, on the other hand, the rapid rotation of the massive young star forming at the center of the cloud wound the magnetic field tighter and tighter, boosting the magnetic field strength up to 1,000 Gauss. The strong magnetic field prevented the cloud from fragmenting further, and the few small protostars that started to form dissipated entirely, leaving only the massive protostar at the end of the simulation. This result suggests that even a weak magnetic field can be amplified enough to stop small protostars from forming, meaning that the first stars may have all formed alone.

The number of protostellar fragments formed (top) and the overall mass of protostars formed (bottom) in all simulations.

Credit: Adapted from Hirano & Machida 2022

Citation

“Exponentially Amplified Magnetic Field Eliminates Disk Fragmentation around Population III Protostars,” Shingo Hirano and Masahiro N. Machida 2022 ApJL 935 L16. doi:10.3847/2041-8213/ac85e0

By Kerry Hensley

Source: American Astronomical Society - AAS Nova

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NASA’s Webb Takes Its First-Ever Direct Image of Distant World

This image shows the exoplanet HIP 65426 b in different bands of infrared light, as seen from the James Webb Space Telescope: purple shows the NIRCam instrument’s view at 3.00 micrometers, blue shows the NIRCam instrument’s view at 4.44 micrometers, yellow shows the MIRI instrument’s view at 11.4 micrometers, and red shows the MIRI instrument’s view at 15.5 micrometers. These images look different because of the ways the different Webb instruments capture light. A set of masks within each instrument, called a coronagraph, blocks out the host star’s light so that the planet can be seen. The small white star in each image marks the location of the host star HIP 65426, which has been subtracted using the coronagraphs and image processing. The bar shapes in the NIRCam images are artifacts of the telescope’s optics, not objects in the scene.. (Unlabeled version) Credit: NASA/ESA/CSA, A Carter (UCSC), the ERS 1386 team, and A. Pagan (STScI).

“This is a transformative moment, not only for Webb but also for astronomy generally,” said Sasha Hinkley, associate professor of physics and astronomy at the University of Exeter in the United Kingdom, who led these observations with a large international collaboration. Webb is an international mission led by NASA in collaboration with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

The exoplanet in Webb’s image, called HIP 65426 b, is about six to 12 times the mass of Jupiter, and these observations could help narrow that down even further. It is young as planets go — about 15 to 20 million years old, compared to our 4.5-billion-year-old Earth.

Astronomers discovered the planet in 2017 using the SPHERE instrument on the European Southern Observatory’s Very Large Telescope in Chile and took images of it using short infrared wavelengths of light. Webb’s view, at longer infrared wavelengths, reveals new details that ground-based telescopes would not be able to detect because of the intrinsic infrared glow of Earth’s atmosphere.

Researchers have been analyzing the data from these observations and are preparing a paper they will submit to journals for peer review. But Webb’s first capture of an exoplanet already hints at future possibilities for studying distant worlds.

Since HIP 65426 b is about 100 times farther from its host star than Earth is from the Sun, it is sufficiently distant from the star that Webb can easily separate the planet from the star in the image.

Webb’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) are both equipped with coronagraphs, which are sets of tiny masks that block out starlight, enabling Webb to take direct images of certain exoplanets like this one. NASA’s Nancy Grace Roman Space Telescope, slated to launch later this decade, will demonstrate an even more advanced coronagraph.

“It was really impressive how well the Webb coronagraphs worked to suppress the light of the host star,” Hinkley said.

Taking direct images of exoplanets is challenging because stars are so much brighter than planets. The HIP 65426 b planet is more than 10,000 times fainter than its host star in the near-infrared, and a few thousand times fainter in the mid-infrared.

In each filter image, the planet appears as a slightly differently shaped blob of light. That is because of the particulars of Webb’s optical system and how it translates light through the different optics.

“Obtaining this image felt like digging for space treasure,” said Aarynn Carter, a postdoctoral researcher at the University of California, Santa Cruz, who led the analysis of the images. “At first all I could see was light from the star, but with careful image processing I was able to remove that light and uncover the planet.”

While this is not the first direct image of an exoplanet taken from space – the Hubble Space Telescope has captured direct exoplanet images previously – HIP 65426 b points the way forward for Webb’s exoplanet exploration.

“I think what’s most exciting is that we’ve only just begun,” Carter said. “There are many more images of exoplanets to come that will shape our overall understanding of their physics, chemistry, and formation. We may even discover previously unknown planets, too.”

– Elizabeth Landau, NASA Headquarters

Alise Fisher
Posted on September 1, 2022
James Webb Space Telescope

Source: NASA/ James Webb Space Telescope

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Massive Stars’ Blasts Hitting Orion’s “Sword” Mapped in Unprecedented Detail Using Hawaiʻi Telescope

Infrared image of orion's photo-dissociation region captured by the Keck ii telescope
Credit: Habart et al./W. M. Keck Observatory

Maunakea, Hawaiʻi – Astronomers using W. M. Keck Observatory on Hawaiʻi Island have captured from Maunakea the most detailed and complete images ever taken of the zone where the famed constellation of Orion gets zapped with ultraviolet (UV) radiation from massive young stars.

This irradiated neutral zone, called a Photo-Dissociation Region (PDR), is located in the Orion Bar within the Orion Nebula, an active star-forming site found in the middle of the “sword” hanging from Orion’s “belt.” When viewed with the naked eye, the nebula is often mistaken for one of the stars in the constellation; when viewed with a telescope, the photogenic nebula is seen as a glowing gaseous stellar nursery located 1,350 light-years from Earth.

“It was thrilling being the first, together with my colleagues of the ‘PDRs4All’ James Webb Space Telescope team, to see the sharpest images of the Orion Bar ever taken in the near infrared,” said Carlos Alvarez, a staff astronomer at Keck Observatory and co-author of the study.

Because the Orion Nebula is the closest massive star formation region to us and may be similar to the environment in which our solar system was born, studying its PDR – the area that’s heated by starlight – is an ideal place to find clues as to how stars and planets are created.

“Observing photo-dissociation regions is like looking into our past,” said Emilie Habart, an Institut d’Astrophysique Spatiale associate professor at Paris-Saclay University and lead author of a paper on this study. “These regions are important because they allow us to understand how young stars influence the gas and dust cloud they are born in, particularly sites where stars, like the Sun, form.”

The study has been accepted for publication in the journal Astronomy & Astrophysics, and is available in preprint format on arXiv.org.

These pathfinder observations have assisted in the planning of the James Webb Space Telescope (JWST) Early Release Science (ERS) program PDRs4All: Radiative feedback of massive stars (ID1288). The PDRs4All program is described in a Publications of the Astronomical Society of the Pacific paper by Berné, Habart, Peeters et al. (2022).

Methodology

To probe Orion’s PDR, the PDRs4All team used Keck Observatory’s second generation Near-Infrared Camera (NIRC2) in combination with the Keck II telescope’s adaptive optics system. They successfully imaged the region with such extreme detail, the researchers were able to spatially resolve and distinguish the Orion Bar’s different substructures – such as ridges, filaments, globules, and proplyds (externally illuminated photoevaporating disks around young stars) – that formed as starlight blasted and sculpted the nebula’s mixture of gas and dust.

Left: Hubble Space Telescope mosaic of the Orion Bar. Credit: NASA/STScI/Rice Univ./C.O’Dell et al. The NIRC2 wide camera Field of View is shown in the yellow square. Right: Infrared heat map of the Orion Bar obtained with Keck Observatory’s NIRC2 instrument reveals substructures such as proplyds. Credit: Habart et al./W. M. Keck Observatory

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“Never before have we been able to observe at a small scale how interstellar matter structures depend on their environments, particularly how planetary systems could form in environments strongly irradiated by massive stars,” said Habart. “This may allow us to better understand the heritage of the interstellar medium in planetary systems, namely our origins.”

Massive young stars emit large quantities of UV radiation that affect the physics and chemistry of their local environment; how this surge of energy the stars inject into their native cloud impacts and shapes star formation is not yet well known.

The new Keck Observatory images of the Orion Bar will help deepen astronomers’ understanding of this process because they reveal in detail where gas in its PDR changes from hot ionized gas, to warm atomic, to cold molecular gas. Mapping this conversion is important because the dense, cold molecular gas is the fuel needed for star formation.

Source:  W. M. Keck Observatory

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What's Next

These new observations from Keck Observatory have informed plans for JWST observations of the Orion Bar, which is among JWST’s targets and is expected to be observed in the coming weeks.

“One of the most exciting aspects of this work is seeing Keck play a fundamental role in the JWST era,” said Alvarez. “JWST will be able to dive deeper into the Orion Bar and other PDRs, and Keck will be instrumental in validating JWST’s early science results. Together, the two telescopes can provide unique insight into the characteristics of the gas and chemical composition of PDRs, which will help us understand the nature of these fascinating star-blasted regions.”

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About NIRC2

The Near-Infrared Camera, second generation (NIRC2) works in combination with the Keck II adaptive optics system to obtain very sharp images at near-infrared wavelengths, achieving spatial resolutions comparable to or better than those achieved by the Hubble Space Telescope at optical wavelengths. NIRC2 is probably best known for helping to provide definitive proof of a central massive black hole at the center of our galaxy. Astronomers also use NIRC2 to map surface features of solar system bodies, detect planets orbiting other stars, and study detailed morphology of distant galaxies.

About Adaptive Optics

W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere.  Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and current systems now deliver images three to four times sharper than the Hubble Space Telescope at near-infrared wavelengths. AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors. Support for this technology was generously provided by the Bob and Renee Parsons Foundation, Change Happens Foundation, Gordon and Betty Moore Foundation, Mt. Cuba Astronomical Foundation, NASA, NSF, and W. M. Keck Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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A Cosmic Tarantula, Caught by NASA’s Webb

Tarantula Nebula (NIRCam Image)
Credits: Image: NASA, ESA, CSA, STScI, Webb ERO Production Team

Tarantula Nebula (MIRI Image)
Credits: Image: NASA, ESA, CSA, STScI, Webb ERO Production Team

Two Views of the Tarantula Nebula (NIRCam and MIRI images)
Credits: Image: NASA, ESA, CSA, STScI, Webb ERO Production Team

Tarantula Nebula (NIRSpec IFU)
Credits: Illustration: NASA, ESA, CSA, STScI, Webb ERO Production Team

Release Images

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Once upon a space-time, a cosmic creation story unfolded: Thousands of never-before-seen young stars spotted in a stellar nursery called 30 Doradus, captured by NASA’s James Webb Space Telescope. Nicknamed the Tarantula Nebula for the appearance of its dusty filaments in previous telescope images, the nebula has long been a favorite for astronomers studying star formation. In addition to young stars, Webb reveals distant background galaxies, as well as the detailed structure and composition of the nebula’s gas and dust.

At only 161,000 light-years away in the Large Magellanic Cloud galaxy, the Tarantula Nebula is the largest and brightest star-forming region in the Local Group, the galaxies nearest our Milky Way. It is home to the hottest, most massive stars known. Astronomers focused three of Webb’s high-resolution infrared instruments on the Tarantula. Viewed with Webb’s Near-Infrared Camera (NIRCam), the region resembles a burrowing tarantula’s home, lined with its silk. The nebula’s cavity centered in the NIRCam image has been hollowed out by blistering radiation from a cluster of massive young stars, which sparkle pale blue in the image. Only the densest surrounding areas of the nebula resist erosion by these stars’ powerful stellar winds, forming pillars that appear to point back toward the cluster. These pillars contain forming protostars, which will eventually emerge from their dusty cocoons and take their turn shaping the nebula. 

Webb’s Near-Infrared Spectrograph (NIRSpec) caught one very young star doing just that. Astronomers previously thought this star might be a bit older and already in the process of clearing out a bubble around itself. However, NIRSpec showed that the star was only just beginning to emerge from its pillar and still maintained an insulating cloud of dust around itself. Without Webb’s high-resolution spectra at infrared wavelengths, this episode of star formation-in-action could not have been revealed. 

The region takes on a different appearance when viewed in the longer infrared wavelengths detected by Webb’s Mid-infrared Instrument (MIRI). The hot stars fade, and the cooler gas and dust glow. Within the stellar nursery clouds, points of light indicate embedded protostars, still gaining mass. While shorter wavelengths of light are absorbed or scattered by dust grains in the nebula, and therefore never reach Webb to be detected, longer mid-infrared wavelengths penetrate that dust, ultimately revealing a previously unseen cosmic environment.  

One of the reasons the Tarantula Nebula is interesting to astronomers is that the nebula has a similar type of chemical composition as the gigantic star-forming regions observed at the universe’s “cosmic noon,” when the cosmos was only a few billion years old and star formation was at its peak. Star-forming regions in our Milky Way galaxy are not producing stars at the same furious rate as the Tarantula Nebula, and have a different chemical composition. This makes the Tarantula the closest (i.e., easiest to see in detail) example of what was happening in the universe as it reached its brilliant high noon. Webb will provide astronomers the opportunity to compare and contrast observations of star formation in the Tarantula Nebula with the telescope’s deep observations of distant galaxies from the actual era of cosmic noon.

Despite humanity’s thousands of years of stargazing, the star-formation process still holds many mysteries – many of them due to our previous inability to get crisp images of what was happening behind the thick clouds of stellar nurseries. Webb has already begun revealing a universe never seen before, and is only getting started on rewriting the stellar creation story.  

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

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Credits:

Release: NASA, ESA, CSA, STScI

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Source:NASA's James Webb Space Telescope/News

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Galactic Overlap

LEDA 2073461
Credit: ESA/Hubble & NASA, W. Keel

Two overlapping spiral galaxies are pictured in this image from the NASA/ESA Hubble Space Telescope. The two galaxies, which have the uninspiring names SDSS J115331 and LEDA 2073461, lie more than a billion light-years from Earth. Despite appearing to collide in this image, the alignment of the two galaxies is likely just by chance — the two are not actually interacting. While these two galaxies might simply be ships that pass in the night, Hubble has captured a dazzling array of interacting galaxies in the past.

This image is one of many Hubble observations delving into highlights of the Galaxy Zoo project. Originally established in 2007, the Galaxy Zoo project and its successors are massive citizen science projects which crowdsource galaxy classifications from a pool of hundreds of thousands of volunteers. These volunteers classify galaxies imaged by robotic telescopes and are often the first to ever set eyes on an astronomical object.

Over the course of the original Galaxy Zoo project, volunteers discovered a menagerie of weird and wonderful galaxies such as unusual 3-armed spiral galaxies and colliding ring galaxies. The astronomers coordinating the project applied for Hubble time to observe the most unusual inhabitants of the Galaxy Zoo — but true to the project’s crowdsourced roots, the list of targets was chosen by a public vote.

Source: ESA/Hubble/potw

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VLBA Produces First Full 3-D View of Binary Star-Planet System

From above a planet about twice the size of Jupiter, this artist's conception shows the star that planet is orbiting and that star's binary companion in the distance. Credit: Sophia Dagnello, NRAO/AUI/NSF. Hi-Res File

In this artist's conception, a small star (orange) is orbited by a Jupiter-like planet (blue), and by a more-distant companion star (red). Credit: Sophia Dagnello, NRAO/AUI/NSF.

Hi-Res File

Two Stars and a Planet

Artist's animation illustrates the orbital motions of a binary star pair and a planet orbiting one of the stars. Credit: Sophia Dagnello, NRAO/AUI/NSF.

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By precisely tracing a small, almost imperceptible, wobble in a nearby star’s motion through space, astronomers have discovered a Jupiter-like planet orbiting that star, which is one of a binary pair. Their work, using the National Science Foundation’s Very Long Baseline Array (VLBA), produced the first-ever determination of the complete, 3-dimensional structure of the orbits of a binary pair of stars and a planet orbiting one of them. This achievement, the astronomers said, can provide valuable new insights on the process of planet formation.

Though more than 5,000 extrasolar planets have been discovered so far, only three have been discovered using the technique — called astrometry — that produced this discovery. However, the feat of determining the 3-D architecture of a binary-star system that includes a planet “cannot be achieved with other exoplanet discovery methods,” said Salvador Curiel, of the National Autonomous University of Mexico (UNAM).

“Since most stars are in binary or multiple systems, being able to understand systems such as this one will help us understand planet formation in general,” Curiel said.

The two stars, which together are called GJ 896AB, are about 20 light-years from Earth — close neighbors by astronomical standards. They are red dwarf stars, the most common type in our Milky Way galaxy. The larger one, around which the planet orbits, has about 44 percent of the mass of our Sun, while the smaller is about 17 percent as massive as the Sun. They are separated by about the distance of Neptune from the Sun, and orbit each other once every 229 years.

 

The astronomers calculated that the planet has about twice the mass of Jupiter and orbits the star every 284 days. Its distance from the star is slightly less than Venus’ distance from the Sun. The planet’s orbit is inclined roughly 148 degrees from the orbits of the two stars.

“This means that the planet moves around the main star in the opposite direction to that of the secondary star around the main star,” said Gisela Ortiz-León, of UNAM and the Max Planck Institute for Radioastronomy. “This is the first time that such dynamical structure has been observed in a planet associated with a compact binary system that presumably was formed in the same protoplanetary disk,” she added.

“Additional detailed studies of this and similar systems can help us gain important insights into how planets are formed in binary systems. There are alternate theories for the formation mechanism, and more data can possibly indicate which is most likely,” said Joel Sanchez-Bermudez, of UNAM. “In particular, current models indicate that such a large planet is very unlikely as a companion to such a small star, so maybe those models need to be adjusted,” he added.

The astrometric technique will be a valuable tool for characterizing more planetary systems, the astronomers said. “We can do much more work like this with the planned Next Generation VLA (ngVLA),” said Amy Mioduszewski, of the National Radio Astronomy Observatory. “With it, we may be able to find planets as small as the Earth.”

The astronomers are reporting their findings in the 1 September issue of the Astronomical Journal.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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Source: National Radio Astronomy Observatory (NRAO)/News

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Milky Way is Somewhat Normal but not Completely Normal

Figure 1: One of nine observed galaxies (NGC 3338). This spiral galaxy is about 76 million light-years away with a mass similar to the Milky Way. High resolution image is here . Credit: NAOJ

New observations of nine distant galaxies taken with the Subaru Telescope show that the swarms of smaller satellite galaxies around the main galaxies have important similarities and differences compared to the satellite galaxies around the Milky Way. This shows that the Milky Way is a somewhat normal galaxy, but not completely normal. This result is important for understanding to what extent we can apply what we know about the local environment to the rest of the Universe.

Astronomers are always trying to figure out how much of what we see in the skies is typical, and how much is unique to the local area. Just as the ability to study planets around other stars has given us new insights about the planets in the Solar System, astronomers can now observe distant galaxies in detail and compare them to what we know about the Milky Way.

Large galaxies such as the Milky Way are surrounded by smaller satellite galaxies. More than 50 satellite galaxies have been detected around the Milky Way, many less than theoretically expected. Also, the Milky Way’s satellite galaxies are found clustered together, while predictions indicate that they should be evenly distributed.

A group led by researchers at the National Astronomical Observatory of Japan (NAOJ) used the Subaru Telescope to take images of nine galaxies with masses similar to the Milky Way, each about 50 to 80 million light-years away. In these images, the group successfully detected 93 candidates for faint, small satellite galaxies. The number of satellites per main galaxy varied greatly but was comparable to the number of satellite galaxies around the Milky Way, indicating that the Milky Way is normal in terms of its number of satellites. Also, the satellite galaxies were evenly distributed around the main galaxies; matching predictions but not matching what we know about the Milky Way.

Figure 2: A selection of detected satellite galaxies. Most of the satellite galaxies are faint and extended. Zoomhere. Credit: NAOJ

Masashi Nashimoto, a research fellow at NAOJ (currently a JSPS research fellow at the University of Tokyo), commented: "These results are valuable information for statistically examining various issues related to satellite galaxies. On the other hand, some objects were not clearly identified as satellite galaxies, and we expect to identify them by further observations."

Satellite galaxies provide clues to how the main galaxy formed, so improving our understanding of them helps us to understand the evolution of galaxies in general, and the Milky Way in particular, which created the conditions where the Earth and life could form.

These results appeared as Nashimoto et al. "The Missing Satellite Problem outside of the Local Group. II. Statistical Properties of Satellites of Milky Way-like Galaxies" in the Astrophysical Journal on August 29, 2022.

Source: Subaru Telescope

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