CfA Scientists Play Important Role in New NASA Mission

This artist's impression of SPHEREx shows the spacecraft as it will appear when in low-Earth orbit. During its 27-month nominal mission, SPHEREx will conduct four all-sky surveys to study the early history of the cosmos and search for interstellar molecules such as water and other compounds thought to be precursors of life as we know it.  Credit: NASA/JPLM High Resolution Image

A new NASA mission with major roles from scientists at the Center for Astrophysics | Harvard & Smithsonian (CfA) will help answer questions about why the large scale structure of the Universe looks the way it does today, how galaxies form and evolve, and what are the abundances of water and other key ingredients for life in our Galaxy.

SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) will identify specific atoms and molecules in millions of objects across space using their unique signatures in optical and infrared spectra, which show how their light depends on wavelength.

After its launch into space on March 11, 2025 from the Vandenberg Space Force Base in California, SPHEREx will survey the entire sky four times over its 25-month mission. Astronomers will be able to combine SPHEREx’s ability to scan large sections of the sky quickly with more targeted studies Harvard-Smithsonian Center for Astrophysics (CfA) from ground-based telescopes and others in space like NASA’s James Webb Space Telescope (JWST).

The CfA will lead the investigation into the abundances and distributions of molecules that are vital for life. Specifically, SPHEREx will conduct a survey along almost 10 million lines of sight in the Milky Way and the Magellanic Clouds, neighboring galaxies to our own. This survey will reveal crucial life-enabling molecules like water (H₂O), carbon monoxide (CO), and carbon dioxide (CO₂) in their icy states on the surfaces of interstellar dust grains.

These data will enable CfA scientists to evaluate the ice content in each direction and will help to trace the evolution of these ices as they transition from molecular clouds to planet-forming disks and, ultimately, to newly forming planets.  JWST can follow up the most interesting targets identified by SPHEREx, making the two facilities a particularly powerful combination for studying how Solar System planets as well as planets around other stars get their key ingredients for life.

The CfA SPHEREx team is led by Dr.Gary Melnick and includes Drs. Matthew Ashby, Joseph Hora, and Volker Tolls, who are joined by visiting scientist, Dr. Jaeyeong Kim, from the Korean Astronomy and Space Science Institute.

SPHEREx’ data will be freely available to scientists around the world, providing new information about hundreds of millions of cosmic objects. More about SPHEREx at the CfA can be found at https://www.cfa.harvard.edu/facilities-technology/telescopes-instruments/spherex

Source: Harvard-Smithsonian Center for Astrophysics (CfA)/News

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NASA's Webb Finds Planet-Forming Disks Lived Longer in Early Universe

Protoplanetary Disks in NGC 346 (NIRCam Image)
Credits/Image: NASA, ESA, CSA, STScI, Olivia C. Jones (UK ATC), Guido De Marchi (ESTEC), Margaret Meixner (USRA)

Protoplanetary Disks in NGC 346 Spectra (NIRSpec)
Credits/Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

NGC 346: Hubble and Webb Observations

Credits/Image: NASA, ESA, CSA, STScI, Olivia C. Jones (UK ATC), Guido De Marchi (ESTEC), Margaret Meixner (USRA), Antonella Nota (ESA)

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NASA’s James Webb Space Telescope just solved a conundrum by proving a controversial finding made with the agency’s Hubble Space Telescope more than 20 years ago.

In 2003, Hubble provided evidence of a massive planet around a very old star, almost as old as the universe. Such stars possess only small amounts of heavier elements that are the building blocks of planets. This implied that some planet formation happened when our universe was very young, and those planets had time to form and grow big inside their primordial disks, even bigger than Jupiter. But how? This was puzzling.

To answer this question, researchers used Webb to study stars in a nearby galaxy that, much like the early universe, lacks large amounts of heavy elements. They found that not only do some stars there have planet-forming disks, but that those disks are longer-lived than those seen around young stars in our Milky Way galaxy.

“With Webb, we have a really strong confirmation of what we saw with Hubble, and we must rethink how we model planet formation and early evolution in the young universe,” said study leader Guido De Marchi of the European Space Research and Technology Centre in Noordwijk, Netherlands.

A Different Environment in Early Times

In the early universe, stars formed from mostly hydrogen and helium, and very few heavier elements such as carbon and iron, which came later through supernova explosions.

“Current models predict that with so few heavier elements, the disks around stars have a short lifetime, so short in fact that planets cannot grow big,” said the Webb study’s co-investigator Elena Sabbi, chief scientist for Gemini Observatory at the National Science Foundation’s NOIRLab in Tucson. "But Hubble did see those planets, so what if the models were not correct and disks could live longer?"

To test this idea, scientists trained Webb on the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s nearest neighbors. In particular, they examined the massive, star-forming cluster NGC 346, which also has a relative lack of heavier elements. The cluster served as a nearby proxy for studying stellar environments with similar conditions in the early, distant universe.

Hubble observations of NGC 346 from the mid 2000s revealed many stars about 20 to 30 million years old that seemed to still have planet-forming disks around them. This went against the conventional belief that such disks would dissipate after 2 or 3 million years.

“The Hubble findings were controversial, going against not only empirical evidence in our galaxy but also against the current models,” said De Marchi. “This was intriguing, but without a way to obtain spectra of those stars, we could not really establish whether we were witnessing genuine accretion and the presence of disks, or just some artificial effects.”

Now, thanks to Webb’s sensitivity and resolution, scientists have the first-ever spectra of forming, Sun-like stars and their immediate environments in a nearby galaxy.

“We see that these stars are indeed surrounded by disks and are still in the process of gobbling material, even at the relatively old age of 20 or 30 million years,” said De Marchi. “This also implies that planets have more time to form and grow around these stars than in nearby star-forming regions in our own galaxy.”

A New Way of Thinking

This finding refutes previous theoretical predictions that when there are very few heavier elements in the gas around the disk, the star would very quickly blow away the disk. So the disk’s life would be very short, even less than a million years. But if a disk doesn't stay around the star long enough for the dust grains to stick together and pebbles to form and become the core of a planet, how can planets form?

The researchers explained that there could be two distinct mechanisms, or even a combination, for planet-forming disks to persist in environments scarce in heavier elements.

First, to be able to blow away the disk, the star applies radiation pressure. For this pressure to be effective, elements heavier than hydrogen and helium would have to reside in the gas. But the massive star cluster NGC 346 only has about ten percent of the heavier elements that are present in the chemical composition of our Sun. Perhaps it simply takes longer for a star in this cluster to disperse its disk.

The second possibility is that, for a Sun-like star to form when there are few heavier elements, it would have to start from a larger cloud of gas. A bigger gas cloud will produce a bigger disk. So there is more mass in the disk and therefore it would take longer to blow the disk away, even if the radiation pressure were working in the same way.

“With more matter around the stars, the accretion lasts for a longer time,” said Sabbi. "The disks take ten times longer to disappear. This has implications for how you form a planet, and the type of system architecture that you can have in these different environments. This is so exciting.”

The science team’s paper appears in the Dec. 16 issue of The Astrophysical Journal.

The James Webb Space Telescope is the world's premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing 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 CSA (Canadian Space Agency).

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt manages the telescope and mission operations. Lockheed Martin Space, based in Denver also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Source: Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Ann Jenkins
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• The science paper by Guido De Marchi et al.

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Distant Stars Spotted for the First Time in the Vast Magellanic Stream

Artist's rendition of the Magellanic Stellar Stream. The Milky Way's nearest neighboring galaxies - the Small and Large Magellanic Clouds - are shown on the right side of the illustration. As these galaxies move to the right, the gaseous Magellanic Stream billows behind them, intertwining and stretching across the southern sky. The illustration also shows the 13 red giant stars discovered in the Magellanic Stellar Stream. Image Credits: CfA / Melissa Weiss. High Resolution Image / Low Resolution Image

All-sky map of stars observed by the Gaia space observatory in 'galactic' coordinates, looking towards the center of the Milky Way. The neutral hydrogen gas of the Magellanic Stream is displayed in blue, spanning almost the entire southern sky. Red stars indicate the thirteen red giant stars identified by Chandra et al. to be members of the Magellanic Stellar Stream.  Credit: Red giants: CfA/Vedant Chandra/Melissa Weiss. All-sky view: Gaia Data Processing and Analysis Consortium (DPAC); A. Moitinho/A. F. Silva/M. Barros/C. Barata, University of Lisbon, Portugal; H. Savietto, Fork Research, Portugal. Magellanic Stream data: D. Nidever et al., NRAO/AUI/NSF, Leiden-Argentine-Bonn Survey; Parkes, Westerbork, and Arecibo Observatories. High Resolution Image / Low Resolution Image

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Astronomers have solved a half-century-old scientific mystery by identifying stars associated with the cosmic gas stream emanating from a pair of nearby galaxies.

Cambridge, Mass. – For nearly fifty years, astronomers have come up empty-handed in their search for stars within the sprawling structure known as the Magellanic Stream. A colossal ribbon of gas, the Magellanic Stream spans nearly 300 Moon diameters across the Southern Hemisphere’s sky, trailing behind the Magellanic Cloud galaxies, two of our Milky Way Galaxy’s closest cosmic neighbors.

Now the star search is finally over. Researchers at the Center for Astrophysics | Harvard & Smithsonian (CfA) and colleagues have identified 13 stars whose distances, motion, and chemical makeup place the stars squarely within the enigmatic stream.

Locating these stars has now pinned down the true distance to the Magellanic Stream, revealing that it extends from 150,000 light-years to more than 400,000 light-years away. The findings pave the way to map and model the Magellanic Stream in unprecedented detail, offering new insights into the history and characteristics of our Galaxy and its neighbors.

"The Magellanic Stream dominates the Southern Hemisphere's sky and our work has at last found a stellar structure that people have sought for decades," says Vedant Chandra, a PhD student in Astronomy & Astrophysics at the CfA and lead author of a new study published in The Astrophysical Journal reporting the findings.

"With these results and more like them, we hope to gain a far greater understanding of the formation of the Magellanic Stream and the Magellanic Clouds, as well as their past and future interactions with our Galaxy," said co-author Charlie Conroy, a Professor of Astronomy at the CfA and Chandra’s advisor.

The Large and Small Magellanic Clouds are dwarf satellite galaxies of the Milky Way. Visible to the naked eye as gauzy luminances, the Clouds have been known since antiquity. With the advent of increasingly powerful telescopes able to perceive phenomena too faint for our eyes to see, astronomers discovered a gigantic plume of hydrogen gas apparently cast out of the Clouds in the early 1970s.

Studies of the gas within this Magellanic Stream further showed the Stream to have two interwoven filaments, with one originating from each Cloud. These features suggest the gravity of the Milky Way might have pulled the Magellanic Stream out of the Clouds. Yet how exactly the Stream formed has remained difficult to nail down, in no small part because of its presumed stellar component remaining irksomely indiscernible.

Chandra came at this problem through an ambitious project started in 2021 for his PhD at the CfA. Chandra consulted with Conroy about interesting topic areas to study, and Conroy pointed Chandra to the uncharted frontier of the Milky Way. The scant stars dotting the Galaxy’s outskirts have been little studied because our Solar System is smack dab in the starry disk of the Milky Way itself—akin to a concertgoer near the stage attempting to see somebody all the way out at the crowd’s periphery.

Over the last decade though, deep observational catalogs compiled by new instruments—especially the European Space Agency's Gaia spacecraft—have started to spy stellar objects that just might be these elusive frontier stars. With access granted to the 6.5m Magellan Baade Telescope at Las Campanas Observatory in Chile through the CfA and MIT, Chandra undertook a project to perform spectroscopy on 200 far-flung Milky Way stars, which when completed will be the largest such sample set to date.

Spectroscopy involves collecting enough light from an object to detect certain signatures imprinted within the light’s color bands that, like fingerprints, uniquely identify individual chemical elements. These signatures thus disclose the chemical makeup of an object, speaking to its origins. In addition, the signatures shift based on the distance to an object, enabling astronomers to tell where an object, such as a star, is going, and correspondingly where it came from.

In the case of Chandra's study, the spectroscopic analysis revealed a set of 13 stars with distances and velocities that fall right within the range expected for the Magellanic Stream. What’s more, the stars’ chemical abundances matched those of the Magellanic Clouds, for instance by being distinctively deficient in the heavier elements astronomers call metals. “These 13 stars just fell right out of our dataset,” says Rohan Naidu, co-author on the study and former CfA graduate student, currently a Hubble postdoctoral fellow at MIT.

By obtaining solid distance and extent measurements of the Magellanic Stream via these stars, the researchers buttressed its origin story as a gravitational grab by the Milky Way. The researchers were additionally able to calculate the Stream's overall gas distribution with higher confidence compared to prior estimates. The distribution indicates that the Stream is actually about twice as massive as generally reckoned.

That result, in turn, presages a future full of new star formation in the Milky Way, because the Stream is actively falling into our Galaxy, according to previous observations. In this way, the Stream serves as a primary provider of the cold, neutral gas needed for making fresh Milky Way stars.

"The Magellanic Stream is the dominant source of stellar calories for the Milky Way—it's our breakfast, lunch, and dinner," says Ana Bonaca, co-author on the study and former ITC postdoctoral fellow at the CfA, now staff scientist at Carnegie Observatories. "Based on the new, higher mass estimates for Magellanic Stream, the Milky Way may end up packing on more pounds than initially thought."

Further studies of the Magellanic Stream should also help astronomers learn more about the composition of our Galaxy. Because the Stream is thought to trace the past paths of the Magellanic Clouds, modeling the evolution of the relatively massive Large Magellanic Cloud via the Stream will improve measurements of the Milky Way’s mass distribution. Much of that mass is in the form of dark matter—a poorly understood, gravity-exerting substance. Better gauging the mass of our Galaxy out in its distant hinterlands will aid in accounting for ordinary matter versus dark matter contents, constraining the possible properties of the latter.

"The beauty of having a vast stellar stream like the Magellanic Stream is that we can now perform so many astrophysical investigations with it," says Chandra. "As our spectroscopic survey continues and we find more stars, we're excited to see what other surprises the Galactic outskirts have in store for us."

Source: Harvard-Smithsonian Center for Astrophysics (CfA)/News

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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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Media Contact:

Peter Edmonds
Interim CfA Public Affairs Officer
Center for Astrophysics | Harvard & Smithsonian
+1 617-571-7279
pedmonds@cfa.harvard.edu

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Ultra-bright X-ray source awakens near a galaxy not so far away

Artist’s impression of an ultra-luminous X-ray pulsar.
NASA / JPL-Caltech - Hi-res image

AstroSat in a clean room before its integration with PSLV-C30 (top panels), and artist's impression of the AstroSat space observatory in orbit (bottom panel). Indian Space Research Organisation (ISRO). Hi-res image

A new ultra-bright source of X-rays has awakened in between our galactic neighbours the Magellanic Clouds, after a 26-year slumber. This is the second-closest such object known to date, with a brightness greater than a million Suns. The discovery is published in the journal Monthly Notices of the Royal Astronomical Society.

The object, known as RX J0209.6-7427, was first detected during a 6-month long outburst in 1993. Though it was initially identified as a Be-type X-ray binary, its true nature remained a mystery as it lingered in a dormant state for the next 26 years, only flaring up again in November last year.

Now, a team of Indian scientists have used AstroSat, India’s first dedicated space observatory, to reveal the extreme nature of the source, and have detected broad-energy X-ray pulsations in the object for the first time. This classifies it as a type of object known as an ultra-luminous X-ray pulsar (ULXP).

The pulsar is located in the Magellanic Bridge, a stream of gas and stars linking the Magellanic Clouds. These are two of our nearest galactic companions, and some of the most distant objects visible to the naked eye. The new X-ray source is the second-closest ULXP known to date, after a 2018 discovery in our own Milky Way galaxy, and is only the eighth such object ever discovered.

Ultra-luminous X-ray sources are observable as single points in the sky, but with brightnesses comparable to entire galaxies. “The conventional theory is that in order to shine so brightly, ULXPs must be glowing accretion discs around black holes,” said Amar Deo Chandra, lead author on the new study. “However, recent discoveries of pulsations in these objects suggest that they may in fact have neutron stars at their heart.”

A neutron star is the remnant of a dead star which contains as much matter as our Sun, but is compressed into a tiny radius of as little as 10km – the size of a small city. The neutron star in this object is thought to be spinning as rapidly as 100 times per second, and emits pulses of energetic X-rays from its magnetic poles, leading to the new ‘X-ray pulsar’ classification.

The group of astronomers, from IISER Kolkata, IUCAA Pune and the Center for Excellence in Basic Sciences (UM-DAE CEBS) Mumbai, have also found that the pulsar may even be speeding up, setting off bright X-ray ‘fireworks’. This is thought to happen when the neutron star captures material from a companion star, injecting energy into the system and speeding up the rotation.

The scarcity of similar sources makes detecting and studying new ULXPs essential for X-ray astronomers seeking to understand the Universe.

“This is only the eighth ULXP detected so far, and the first one near the Magellanic Clouds,” Chandra adds. “It raises the interesting possibility that a significant fraction of ultra-luminous X-ray sources may really be neutron stars accreting at super Eddington rates, rather than black holes as previously thought.”

Source: Royal Astronomical Society (RAS)

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Media contacts

Dr Morgan Hollis
Royal Astronomical Society
Mob: +44 (0)7802 877 700
press@ras.ac.uk

Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7292 3979
Mob: +44 (0)7802 877 699
press@ras.ac.uk

Science contacts

Mr Amar Deo Chandra
Center of Excellence in Space Sciences India
Indian Institute of Science Education and Research
Kolkata, India
Tel: +9 177 38 510 420

Dr Jayashree Roy
IUCAA Pune, India
Tel: +9 179 00 164 536

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Further information

The new work appears in, “Study of Recent outburst in the Be/X-ray binary RX J0209.6-7427 with AstroSat: A new ultraluminous X-ray pulsar in the Magellanic Bridge?”, A.D. Chandra, J. Roy, P.C. Agrawal, M. Choudhury,, Monthly Notices of the Royal Astronomical Society (2020), in press (DOI: 10.1093/mnras/staa1041).

A copy of the paper is available from: https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/staa1041

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Notes for editors

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,400 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

In 2020 the RAS is 200 years old. The Society is celebrating its bicentennial anniversary with a series of events around the UK, including public lectures, exhibitions, an organ recital, a pop-up planetarium, and the culmination of the RAS 200: Sky & Earth project.

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Festive nebulae light up Milky Way Galaxy satellite

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Festive nebulae

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Wide-field image of Magellanic clouds (ground-based image)

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Globular cluster 47 Tucanae and the Small Magellanic Cloud (ground-based image)

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Small Magellanic Cloud (ground-based image)

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Small Magellanic Cloud and SMIDGE survey 

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Videos 

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Zoom in on NGC 248Videos

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The sheer observing power of the NASA/ESA Hubble Space Telescope is rarely better illustrated than in an image such as this. This glowing pink nebula, named NGC 248, is located in the Small Magellanic Cloud, just under 200 000 light-years away and yet can still be seen in great detail.

Our home galaxy, the Milky Way, is part of a collection of galaxies known as the Local Group. Along with the Andromeda Galaxy, the Milky Way is one of the Group’s most massive members, around which many smaller satellite galaxies orbit. The Magellanic Clouds are famous examples, which can easily be seen with the naked eye from the southern hemisphere.

Within the smaller of these satellite galaxies, the Small Magellanic Cloud, the NASA/ESA Hubble Space Telescope captured two festive-looking emission nebulae, conjoined so they appear as one. Intense radiation from the brilliant central stars is causing hydrogen in the nebulae to glow pink.

Together the nebulae are called NGC 248. They were discovered in 1834 by the astronomer Sir John Herschel. NGC 248 is about 60 light-years long and 20 light-years wide. It is among a number of glowing hydrogen nebulae in the Small Magellanic Cloud, which lies in the southern constellation of Tucana (The Toucan), about 200 000 light-years away.

The nebula was observed as part of a Hubble survey, the Small Magellanic cloud Investigation of Dust and Gas Evolution (SMIDGE). In this survey astronomers are using Hubble to probe the Small Magellanic Cloud to understand how its dust — an important component of many galaxies and related to star formation — is different from the dust in the Milky Way.

Thanks to its relative proximity, the Small Magellanic Cloud is a valuable target. It also turns out to have only between a fifth and a tenth of the amount of heavy elements that the Milky Way has, making the dust similar to what we expect to see in galaxies in the earlier Universe.

This allows astronomers to use it as a cosmic laboratory to study the history of the Universe in our cosmic backyard. These observations also help us to understand the history of our own galaxy as most of the star formation happened earlier in the Universe, at a time when the percentage of heavy elements in the Milky Way was much lower than it is now.

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The data used in this image were taken with Hubble’s Advanced Camera for Surveys in September 2015.

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More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image credit: NASA, ESA, STScI, K. Sandstrom (University of California, San Diego), and the SMIDGE team.

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Links

• Images of Hubble
• Link to hubblesite release

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Contacts

Karin Sandstrom
University of California
San Diego, USA
Tel: +1 858-246-0552
Email: kmsandstrom@ucsd.edu

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

Source: ESA/Hubble/News

Hubble unveils monster stars

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R136 observed with WFC3

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Pseudo image of R136

Astronomers using the unique ultraviolet capabilities of the NASA/ESA Hubble Space Telescope have identified nine monster stars with masses over 100 times the mass of the Sun in the star cluster R136. This makes it the largest sample of very massive stars identified to date. The results, which will be published in the Monthly Notices of the Royal Astronomical Society, raise many new questions about the formation of massive stars.

An international team of scientists using the NASA/ESA Hubble Space Telescope has combined images taken with the Wide Field Camera 3 (WFC3) with the unprecedented ultraviolet spatial resolution of the Space Telescope Imaging Spectrograph (STIS) to successfully dissect the young star cluster R136 in the ultraviolet for the first time [1].

R136 is only a few light-years across and is located in the Tarantula Nebula within the Large Magellanic Cloud, about 170 000 light-years away. The young cluster hosts many extremely massive, hot and luminous stars whose energy is mostly radiated in the ultraviolet [2]. This is why the scientists probed the ultraviolet emission of the cluster.

As well as finding dozens of stars exceeding 50 solar masses, this new study was able to reveal a total number of nine very massive stars in the cluster, all more than 100 times more massive as the Sun. However, the current record holder R136a1 does keep its place as the most massive star known in the Universe, at over 250 solar masses. The detected stars are not only extremely massive, but also extremely bright. Together these nine stars outshine the Sun by a factor of 30 million.

The scientists were also able to investigate outflows from these behemoths, which are most readily studied in the ultraviolet. They eject up to an Earth mass of material per month at a speed approaching one percent of the speed of light, resulting in extreme weight loss throughout their brief lives.

“The ability to distinguish ultraviolet light from such an exceptionally crowded region into its component parts, resolving the signatures of individual stars, was only made possible with the instruments aboard Hubble,” explains Paul Crowther from the University of Sheffield, UK, and lead author of the study. “Together with my colleagues, I would like to acknowledge the invaluable work done by astronauts during Hubble’s last servicing mission: they restored STIS and put their own lives at risk for the sake of future science!” [3]

In 2010 Crowther and his collaborators showed the existence of four stars within R136, each with over 150 times the mass of the Sun. At that time the extreme properties of these stars came as a surprise as they exceeded the upper-mass limit for stars that was generally accepted at that time. Now, this new census has shown that there are five more stars with more than 100 solar masses in R136. The results gathered from R136 and from other clusters also raise many new questions about the formation of massive stars as the origin of these behemoths remains unclear [4].

Saida Caballero-Nieves, a co-author of the study, explains: “There have been suggestions that these monsters result from the merger of less extreme stars in close binary systems. From what we know about the frequency of massive mergers, this scenario can’t account for all the really massive stars that we see in R136, so it would appear that such stars can originate from the star formation process.”

In order to find answers about the origin of these stars the team will continue to analyse the gathered datasets. An analysis of new optical STIS observations will also allow them to search for close binary systems in R136, which could produce massive black hole binaries which would ultimately merge, producing gravitational waves.

“Once again, our work demonstrates that, despite being in orbit for over 25 years, there are some areas of science for which Hubble is still uniquely capable,” concludes Crowther.

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Notes

[1] R136 was originally listed in a catalogue of the brightest stars in the Magellanic Clouds compiled at the Radcliffe Observatory in South Africa. It was separated into three components a, b, c at the European Southern Observatory, with R136a subsequently resolved into a group of eight stars (a1-a8) at ESO, and confirmed as a dense star cluster with the NASA/ESA Hubble Space Telescope after the first servicing mission in 1993.

[2] Very massive stars are exclusive to the youngest star clusters because their lifetimes are only 2-3 million years. Only a handful of such stars are known in the entire Milky Way galaxy.

[3] STIS’s capabilities were restored in 2009 by astronauts who successfully comp

leted Serving Mission 4 (SM4), one of the Hubble’s most challenging and intense servicing missions, involving five spacewalks.

[4] The ultraviolet signatures of even more very massive stars have also been revealed in other clusters — examples include star clusters in the dwarf galaxies NGC 3125 and NGC 5253. However, these clusters are too distant for individual stars to be distinguished even with Hubble.

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More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The results were published in the paper “The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of Heii λ1640 in young star clusters” in the Monthly Notices of the Royal Astronomical Society.

The international team of astronomers in this study consists of Paul A. Crowther (Department of Physics and Astronomy, University of Sheffield, Sheffield, UK), S.M. Caballero-Nieves(Department of Physics and Astronomy, University of Sheffield, Sheffield, UK), K.A. Bostroem (Space Telescope Science Institute, Baltimore MD, USA; Department of Physics, University of California, Davis CA, USA), J. Maíz Apellániz (Centro de Astrobiología, CSIC/INTA, Madrid, Spain), F.R.N. Schneider (Department of Physics, University of Oxford, Oxford, UK; Argelanger-Institut fur Astronomie der Universität Bonn, Bonn, Germany), N.R. Walborn(Space Telescope Science Institute, Baltimore MD, USA), C.R. Angus (Department of Physics and Astronomy, University of Sheffield, Sheffield, UK; Department of Physics, University of Warwick, Coventry, UK), I. Brott (Institute for Astrophysics, Vienna, Austria), A. Bonanos (Institute of Astronomy & Astrophysics, National Observatory of Athens, P. Penteli, Greece), A. de Koter (Astronomical Institute Anton Pannekoek, University of Amsterdam, Amsterdam, Netherlands; Institute of Astronomy, Leuven, Belgium), S.E. de Mink (Astronomical Institute Anton Pannekoek, University of Amsterdam, Amsterdam, Netherlands), C.J. Evans (UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK), G. Gräfener (Armagh Observatory, Armagh, UK), A. Herrero (Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Tenerife, Spain), I.D. Howarth (Department of Physics & Astronomy, University College London, London, UK), N. Langer (Argelanger-Institut fur Astronomie der Universität Bonn, Bonn, Germany), D.J. Lennon (European Space Astronomy Centre, ESA, Villanueva de la Cañada, Madrid, Spain), J. Puls (Universitäts-Sternwarte, Munchen, Germany), H. Sana (Space Telescope Science Institute, Baltimore MD, USA; Institute of Astronomy, Leuven, Belgium), J.S. Vink (Armagh Observatory, Armagh, UK).

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Links

• Images of Hubble
• Link to science paper
• Image of R136 taken in 2009
• ESO release on the discovery of R136a1 in 2010

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Contacts

Paul Crowther
University of Sheffield
United Kingdom
Tel: +44-(0)114 222 4291
Email: paul.crowther@sheffield.ac.uk

Saida Caballero-Nieves
University of Sheffield
United Kingdom
Tel: +1 813 400 3765
Email: s.caballero@shef.ac.uk

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

Source:  Hubble Space Telescope

The Magellanic Clouds and an interstellar filament

The Magellanic Clouds and an interstellar filament

Copyright: ESA and the Planck Collaboration

Hi-res Image (PNG)

Portrayed in this image from ESA’s Planck satellite are the two Magellanic Clouds, among the nearest companions of our Milky Way galaxy. The Large Magellanic Cloud, about 160 000 light-years away, is the large red and orange blob close to the centre of the image. The Small Magellanic Cloud, some 200 000 light-years from us, is the vaguely triangular-shaped object to the lower left.

At around ten and seven billion times the mass of our Sun, respectively, these are classed as dwarf galaxies. As a comparison, the Milky Way and another of its neighbours, the Andromeda galaxy, boast masses of a few hundred billion solar masses each.

The Magellanic Clouds are not visible from high northern latitudes and were introduced to European astronomy only at the turn of the 16th century. However, they were known long before by many civilisations in the southern hemisphere, as well as by Middle Eastern astronomers.

Planck detected the dust between the stars pervading the Magellanic Clouds while surveying the sky to study the cosmic microwave background – the most ancient light in the Universe – in unprecedented detail. In fact, Planck detected emission from virtually anything that shone between itself and the cosmic background at its sensitive frequencies.

These foreground contributions include many galaxies, near and far, as well as interstellar material in the Milky Way. Astronomers need to remove them in order to access the wealth of cosmic information contained in the ancient light. But, as a bonus, they can use the foreground observations to learn more about how stars form in galaxies, including our own.

Interstellar dust from the diffuse medium that permeates our Galaxy can be seen as the mixture of red, orange and yellow clouds in the upper part of this image, which belong to a large star-forming complex in the southern constellation, Chameleon.

In addition, a filament can also be seen stretching from the dense clouds of Chameleon, in the upper left, towards the opposite corner of the image.

Apparently located between the two Magellanic Clouds as viewed from Planck, this dusty filament is in fact much closer to us, only about 300 light-years away. The image shows how well this structure is aligned with the galaxy’s magnetic field, which is represented as the texture of the image and was estimated from Planck’s measurements.

By comparing the structure of the magnetic field and the distribution of interstellar dust in the Milky Way, scientists can study the relative distribution of interstellar clouds and the ambient magnetic field. While in the case of the filamentary cloud portrayed in this image, the structure is aligned with the direction of the magnetic field, in the denser clouds where stars form filaments tend to be perpendicular to the interstellar magnetic field.

The lower right part of the image is one of the faintest areas of the sky at Planck’s frequencies, with the blue hues indicating very low concentrations of cosmic dust. Similarly, the eddy-like structure of the texture is caused primarily by instrument noise rather than by actual features in the magnetic field.

The emission from dust is computed from a combination of Planck observations at 353, 545 and 857 GHz, whereas the direction of the magnetic field is based on Planck polarisation data at 353 GHz. The image spans about 40º.

Source: ESA

Giant Intergalactic Gas Stream Longer than Thought

Combined radio/optical image shows Milky Way, Magellanic Clouds, and the new radio image of the Magellanic Stream. Blue and white are the Milky Way and Magellanic Clouds. Red is the hydrogen gas in the Magellanic Stream, in the disks of the Magellanic Clouds, and in the stream's Leading Arm. The Milky Way is horizontal in the middle of the image; the Magellanic Clouds are the light spots at the center-right portion of the image, from which the gas stream originates. Brown is dust clouds in the Milky Way. CREDIT: Nidever, et al., NRAO/AUI/NSF and Meilinger, Leiden-Argentine-Bonn Survey, Parkes Observatory, Westerbork Observatory, Arecibo Observatory. Large image with labels

The astronomers used the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) to fill important gaps in the picture of gas streaming outward from the Magellanic Clouds. The first evidence of such a flow, named the Magellanic Stream, was discovered more than 30 years ago, and subsequent observations added tantalizing suggestions that there was more. However, the earlier picture showed gaps that left unanswered whether this other gas was part of the same system.

"We now have answered that question. The stream is continuous," said David Nidever, of the University of Virginia. "We now have a much more complete map of the Magellanic Stream," he added. The astronomers presented their findings to the American Astronomical Society's meeting in Washington, DC.

The Magellanic Clouds are the Milky Way's two nearest neighbor galaxies, about 150,000 to 200,000 light-years distant from the Milky Way. Visible in the Southern Hemisphere, they are much smaller than our Galaxy and may have been distorted by its gravity.

Nidever and his colleagues observed the Magellanic Stream for more than 100 hours with the GBT. They then combined their GBT data with that from earlier studies with other radio telescopes, including the Arecibo telescope in Puerto Rico, the Parkes telescope in Australia, and the Westerbork telescope in the Netherlands. The result shows that the stream is more than 40 percent longer than previously known with certainty.

One consequence of the added length of the gas stream is that it must be older, the astronomers say. They now estimate the age of the stream at 2.5 billion years.

The revised size and age of the Magellanic Stream also provides a new potential explanation for how the flow got started.

"The new age of the stream puts its beginning at about the time when the two Magellanic Clouds may have passed close to each other, triggering massive bursts of star formation," Nidever explained. "The strong stellar winds and supernova explosions from that burst of star formation could have blown out the gas and started it flowing toward the Milky Way," he said.

"This fits nicely with some of our earlier work that showed evidence for just such blowouts in the Magellanic Clouds," said Steven Majewski, of the University of Virginia.

Earlier explanations for the stream's cause required the Magellanic Clouds to pass much closer to the Milky Way, but recent orbital simulations have cast doubt on such mechanisms.

Nidever and Majewski worked with Butler Burton of the Leiden Observatory and the National Radio Astronomy Observatory, and Lou Nigra of the University of Wisconsin. In addition to presenting the results to the American Astronomical Society, the scientists have submitted a paper to the Astrophysical Journal.

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

Contact:

Dave Finley, Public Information Officer
Socorro, NM
(575) 835-7302
dfinley@nrao.edu