Monday, November 19, 2018

Astronomers Find Possible Elusive Star Behind Supernova

Artist's Illustration of SN 2017ein
Credits: NASA, ESA, and J. Olmsted (STScI)

SN 2017ein in NGC 3938
Credits: NASA, ESA, S. Van Dyk (Caltech), and W. Li (University of California)




Astronomers may have finally uncovered the long-sought progenitor to a specific type of exploding star by sifting through NASA Hubble Space Telescope archival data. The supernova, called a Type Ic, is thought to detonate after its massive star has shed or been stripped of its outer layers of hydrogen and helium.

These stars could be among the most massive known — at least 30 times heftier than our Sun. Even after shedding some of their material late in life, they are expected to be big and bright. So it was a mystery why astronomers had not been able to nab one of these stars in pre-explosion images.

Finally, in 2017, astronomers got lucky. A nearby star ended its life as a Type Ic supernova. Two teams of astronomers pored through the archive of Hubble images to uncover the putative precursor star in pre-explosion photos taken in 2007. The supernova, catalogued as SN 2017ein, appeared near the center of the nearby spiral galaxy NGC 3938, located roughly 65 million light-years away.

This potential discovery could yield insight into stellar evolution, including how the masses of stars are distributed when they are born in batches.

"Finding a bona fide progenitor of a supernova Ic is a big prize of progenitor searching," said Schuyler Van Dyk of the California Institute of Technology (Caltech) in Pasadena, lead researcher of one of the teams. "We now have for the first time a clearly detected candidate object." His team's paper was published in June in The Astrophysical Journal.

A paper by a second team, which appeared in the Oct. 21, 2018, issue of the Monthly Notices of the Royal Astronomical Society, is consistent with the earlier team's conclusions.

"We were fortunate that the supernova was nearby and very bright, about 5 to 10 times brighter than other Type Ic supernovas, which may have made the progenitor easier to find," said Charles Kilpatrick of the University of California, Santa Cruz, leader of the second team. "Astronomers have observed many Type Ic supernovas, but they are all too far away for Hubble to resolve. You need one of these massive, bright stars in a nearby galaxy to go off. It looks like most Type Ic supernovas are less massive and therefore less bright, and that's the reason we haven't been able to find them."

An analysis of the object's colors shows that it is blue and extremely hot. Based on that assessment, both teams suggest two possibilities for the source's identity. The progenitor could be a single hefty star between 45 and 55 times more massive than our Sun. Another idea is that it could have been a massive binary-star system in which one of the stars weighs between 60 and 80 solar masses and the other roughly 48 suns. In this latter scenario, the stars are orbiting closely and interact with each other. The more massive star is stripped of its hydrogen and helium layers by the close companion, and eventually explodes as a supernova.

The possibility of a massive double-star system is a surprise. "This is not what we would expect from current models, which call for lower-mass interacting binary progenitor systems," Van Dyk said.

Expectations on the identity of the progenitors of Type Ic supernovas have been a puzzle. Astronomers have known that the supernovas were deficient in hydrogen and helium, and initially proposed that some hefty stars shed this material in a strong wind (a stream of charged particles) before they exploded. When they didn't find the progenitors stars, which should have been extremely massive and bright, they suggested a second method to produce the exploding stars that involves a pair of close-orbiting, lower-mass binary stars. In this scenario, the heftier star is stripped of its hydrogen and helium by its companion. But the "stripped" star is still massive enough to eventually explode as a Type Ic supernova. "Disentangling these two scenarios for producing Type Ic supernovas impacts our understanding of stellar evolution and star formation, including how the masses of stars are distributed when they are born, and how many stars form in interacting binary systems," explained Ori Fox of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, a member of Van Dyk's team. "And those are questions that not just astronomers studying supernovas want to know, but all astronomers are after."

Type Ic supernovas are just one class of exploding star. They account for about 20 percent of massive stars that explode from the collapse of their cores.

The teams caution that they won't be able to confirm the source's identity until the supernova fades in about two years. The astronomers hope to use either Hubble or the upcoming NASA James Webb Space Telescope to see whether the candidate progenitor star has disappeared or has significantly dimmed. They also will be able to separate the supernova's light from that of stars in its environment to calculate a more accurate measurement of the object's brightness and mass.

SN 2017ein was discovered in May 2017 by Tenagra Observatories in Arizona. But it took the sharp resolution of Hubble to pinpoint the exact location of the possible source. Van Dyk's team imaged the young supernova in June 2017 with Hubble's Wide Field Camera 3. The astronomers used that image to pinpoint the candidate progenitor star nestled in one of the host galaxy's spiral arms in archival Hubble photos taken in December 2007 by the Wide Field Planetary Camera 2.

Kilpatrick's group also observed the supernova in June 2017 in infrared images from one of the 10-meter telescopes at the W. M. Keck Observatory in Hawaii. The team then analyzed the same archival Hubble photos as Van Dyk's team to uncover the possible source.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). 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.


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Contacts

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Schuyler Van Dyk
Caltech/IPAC, Pasadena, California
626-395-1881
vandyk@ipac.caltech.edu

Charles Kilpatrick
University of California, Santa Cruz, California
831-459-5098
cdkilpat@ucsc.edu


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Sunday, November 18, 2018

Exploding Stars Make Key Ingredient in Sand, Glass

This image of supernova remnant G54.1+0.3 includes radio, infrared and X-ray light. 
Credit: NASA/JPL-Caltech/CXC/ESA/NRAO/J. Rho (SETI Institute) › Full image and caption


We are all, quite literally, made of star dust. Many of the chemicals that compose our planet and our bodies were formed directly by stars. Now, a new study using observations by NASA's Spitzer Space Telescope reports for the first time that silica - one of the most common minerals found on Earth - is formed when massive stars explode.

Look around you right now and there's a good chance you will see silica (silicon dioxide, SiO2) in some form. A major component of many types of rocks on Earth, silica is used in industrial sand-and-gravel mixtures to make concrete for sidewalks, roads and buildings. One form of silica, quartz, is a major component of sand found on beaches along the U.S. coasts. Silica is a key ingredient in glass, including plate glass for windows, as well as fiberglass. Most of the silicon used in electronic devices comes from silica.

In total, silica makes up about 60 percent of Earth's crust. Its widespread presence on Earth is no surprise, as silica dust has been found throughout the universe and in meteorites that predate our solar system. One known source of cosmic dust is AGB stars, or stars with about the mass of the Sun that are running out of fuel and puff up to many times their original size to form a red giant star. (AGB stars are one type of red giant star.) But silica is not a major component of AGB star dust, and observations had not made it clear if these stars could be the primary producer of silica dust observed throughout the universe.

The new study reports the detection of silica in two supernova remnants, called Cassiopeia A and G54.1+0.3. A supernova is a star much more massive than the Sun that runs out of the fuel that burns in its core, causing it to collapse on itself. The rapid in-fall of matter creates an intense explosion that can fuse atoms together to create "heavy" elements, like sulfur, calcium and silicon.

Chemical Fingerprints

To identify silica in Cassiopeia A and G54.1+0.3, the team used archival data from Spitzer's IRS instrument and a technique called spectroscopy, which takes light and reveals the individual wavelengths that compose it. (You can observe this effect when sunlight passes through a glass prism and produces a rainbow: The different colors are the individual wavelengths of light that are typically blended together and invisible to the naked eye.)

Chemical elements and molecules each emit very specific wavelengths of light, meaning they each have a distinct spectral "fingerprint" that high-precision spectrographs can identify. In order to discover the spectral fingerprint of a given molecule, researchers often rely on models (typically done with computers) that re-create the molecule's physical properties. Running a simulation with those models then reveals the molecule's spectral fingerprint.

But physical factors can subtly influence the wavelengths that molecules emit. Such was the case with Cassiopeia A. Although the spectroscopy data of Cassiopeia A showed wavelengths close to what would be expected from silica, researchers could not match the data with any particular element or molecule.

Jeonghee Rho, an astronomer at the SETI Institute in Mountain View, California, and the lead author on the new paper, thought that perhaps the shape of the silica grains could be the source of the discrepancy, because existing silica models assumed the grains were perfectly spherical.

She began building models that included some grains with nonspherical shapes. It was only when she completed a model that assumed all the grains were not spherical but, rather, football-shaped that the model "really clearly produced the same spectral feature we see in the Spitzer data," Rho said.

Rho and her coauthors on the paper then found the same feature in a second supernova remnant, G54.1+0.3. The elongated grains may tell scientists something about the exact processes that formed the silica.

The authors also combined the observations of the two supernova remnants from Spitzer with observations from the European Space Agency's Herschel Space Observatory in order to measure the amount of silica produced by each explosion. Herschel detects different wavelengths of infrared light than Spitzer. The researchers looked at the entire span of wavelengths provided by both observatories and identified the wavelength at which the dust has its peak brightness. That information can be used to measure the temperature of dust, and both brightness and temperature are necessary in order to measure the mass. The new work implies that the silica produced by supernovas over time was significant enough to contribute to dust throughout the universe, including the dust that ultimately came together to form our home planet.

The study was published on Oct. 24, 2018, in the Monthly Notices of the Royal Astronomical Society, and it confirms that every time we gaze through a window, walk down the sidewalk or set foot on a pebbly beach, we are interacting with a material made by exploding stars that burned billions of years ago.

NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory in Pasadena, California. The NASA Herschel Science Center, part of IPAC, supports the U.S. astronomical community. Caltech manages JPL for NASA.

The JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena, California. Spacecraft operations are based at Lockheed Martin Space in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech.

For more information about Herschel and Spitzer, visit:

http://www.herschel.caltech.edu - http://www.spitzer.caltech.edu - https://www.nasa.gov/spitzer


 News Media Contact

 Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Rebecca McDonald
Director of Communications, SETI Institute
650-960-4526
rmcdonald@seti.org


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A Galaxy-scale Fountain of Cold Molecular Gas Pumped by a Black Hole

An image of the bright cluster galaxy Abell 2597 in the X-ray (blue), hydrogen line emission (red), and optical (yellow). Astronomers using multi-wavelength observations from the millimeter to the X-ray have concluded, in agreement with predictions, that this galaxy is both accreting gas from its surroundings and ejecting material out from its supermasssive black hole, thus acting like a cosmic fountain. Credit: X-ray: NASA/CXC/Michigan State Univ/G.Voit et al; Optical: NASA/STScI & DSS; H-alpha: Carnegie Obs./Magellan/W.Baade Telescope/U.Maryland/M.McDona

Most galaxies lie in clusters containing from a few to thousands of other galaxies. Our Milky Way, for example, belongs to the Local Group cluster of about fifty galaxies whose other large member, the Andromeda galaxy, is about 2.3 million light-years away. Clusters are the most massive gravitationally bound objects in the universe and form (according to current ideas) in a "bottoms-up" fashion with smaller structures developing first and with dark matter playing an important role. Exactly how they grow and evolve, however, depends on several competing physical processes including the behavior of the hot intracluster gas.

The galaxy Abell 2597 lies near the center of a cluster about one billion light-years away in the midst of a hot nebula (tens of millions of degrees) of cluster gas. Astronomers have long theorized that intergalactic matter like the plasma around Abell 2597 can fall onto galaxies, cool, and provide fresh material for the galaxy's star formation. They have, however, also discovered the opposite activity: galaxies’ central supermassive black holes are ejecting jets of material back out into the hot intracluster medium. CfA astronomers Grant Tremblay, Paul Nulsen, Esra Bulbul, Laurence David, Bill Forman, Christine Jones, Ralph Kraft, Scott Randall, and John ZuHone led a large team of colleagues studying the behavior of the hot gas and these competing processes in Abell 2597 using a wide range of observations including new and archival ALMA millimeter observations, optical spectroscopy, and deep Chandra X-Ray Observatory images.

The sensitive and wide-ranging datasets enabled the scientists to probe the thermodynamic character and motions of the hot gas (including both infall and outflow streams), the cold, star forming dust clouds in the galaxy, and the relative spatial arrangement of all these ingredients. They find detailed support for the models, including both infall of hot material into the galaxy and its subsequent conversion into new stars and as well the outflow of gas driven by jets from the central supermassive black hole. They show that the warm and cold material are actually found together in this galaxy (although they are of different densities), with clouds of cold gas likely feeding the black hole and apparently coupling to the powerful jets ejected from the nucleus. The result is that the molecular and ionized nebula at the heart of Abell 2597 is what they term a galaxy-scale "fountain:" cold gas drains into the reservoir created by the presence of the black hole at the center, and this powers outflowing jets that, in turn, later cool and sink, raining back down. Because the outflowing material does not move quickly enough to escape the galaxy's gravity, they conclude that this dramatic galactic fountain seems likely to be long-lived. It may also be a common occurrence in these massive clusters, helping to explain the cosmic evolution of galaxies.

Reference(s):

"A Galaxy-scale Fountain of Cold Molecular Gas Pumped by a Black Hole," G. R. Tremblay et al. ApJ 865, 13, 2018.



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Saturday, November 17, 2018

Comet 17P/Holmes which exhibited a Great Outburst in October 2007 was Born in a Region of the Solar Nebula Far from the Sun

Figure 1: Mid-infrared image of Comet 17P/Holmes on October 25, 2007. The mid-infrared observations of the comet by COMICS on the Subaru Telescope were carried out for four consecutive nights from two days to five days after its great outburst on October 23, 2007 UT. (Credit: NAOJ)

A team of astronomers led by Yoshiharu Shinnaka of Koyama Astronomical Observatory of Kyoto Sangyo University, Japan, has discovered that Comet 17P/Holmes formed in a cold region of the solar nebula far from the Sun. This suggests that Comet 17P/Holmes probably includes highly volatile species abundantly (with low sublimation temperatures below ~50 K) and that sublimation of these volatiles could be responsible for the comet's explosive releases of dust grains. These new insights come from re-analysing mid-infrared spectra of the comet taken by the Cooled Mid-Infrared Camera and Spectrograph (COMICS) on the Subaru Telescope during October 25 to 28, 2007.

Comet 17P/Holmes is a short-period comet with an orbital period of ~7 years. The comet underwent a great outburst starting on October 23, 2007 (when the comet was 2.5 au from the Sun), five months after perihelion at 2.05 au on May 5, 2007. The total magnitude of this outburst reached a maximum brightness of ~2-3 mag in V-band within two days after the outburst, increasing from an initial brightness of ~17 mag. This huge outburst, with a 15 mag brightness increase, was unlike any other. Other than the outburst in 2007, Comet 17P/Holmes had exhibited outbursts in November 1892, when the comet was discovered by E. Holmes, and January 1893.

This research focuses on the dust components released from Comet 17P/Holmes. A cometary nucleus includes minerals called silicates. Cometary silicates consist of both amorphous and crystalline forms. Silicates in amorphous form exist in interstellar space and might have been incorporated into the cometary nucleus in the solar nebula in the early Solar System. Meanwhile, it has been thought that crystalline silicates formed by the annealing of amorphous silicate grains or direct condensation of gaseous materials in hot regions of the solar nebula near the Sun and were incorporated into cometary nuclei in the cold comet-forming region (~5—30 au from the Sun) after radial transportation of the silicate grains in the solar nebula. Because the mass fraction of crystalline silicates with respect to the total (amorphous + crystalline) silicates is expected to be smaller for further distances from the Sun in the solar nebula, it is thought that a smaller mass fraction of crystalline silicates in a comet indicates that the comet formed at a further distance from the Sun in the solar nebula.

The researchers found that dust grains of Comet 17P/Holmes contain a large amount of amorphous silicates (less crystalline silicates) compared with grains of other comets. This result is evidence that Comet 17P/Holmes formed in a farther, colder region in the solar nebula than other comets. At such a region, it is expected that much CO ice (which has a low sublimation temperature of ~30 K) and amorphous water ices (which through crystallization in the low temperature conditions become an energy source for explosive sublimation) would have existed. 

Figure 2: The mid-infrared spectrum of Comet 17P/Holmes on October 25, 2007. Four striking thermal emission features of silicate dust grains are seen around 10 microns. Narrow peaks originate from crystalline silicate and the peak position depends on the Mg/Fe ratio of the silicate grains. The sets of six vertical lines (red, orange, green, blue, purple, and black in order from left to right) indicate peak wavelengths of the 10.0, 10.4, 11.2 and 11.9 microns lines with Mg/(Mg + Fe) ratios of 100% to 0% in 20% intervals. The vertical gray bar is the absorption band of telluric ozone (O3). (Credit: NAOJ)

These results were published on October 31, 2018 in The Astronomical Journal (Shinnaka et al., 156, 242, "Mid-infrared Spectroscopic Observations of Comet 17P/Holmes Immediately After Its Great Outburst in 2007"). This research paper is also available as a preprint (Shinnaka et al., arxiv: 1808.07606) on arxiv.org. This research is supported by Grants-in-Aid from Japan Society for the Promotion of Science Fellows, 15J10864 (YS) and for Scientific Research (C), 17K05381 (TO). This paper is based on data collected at the Subaru Telescope and obtained from SMOKA, which is operated by the National Astronomical Observatory of Japan.

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Friday, November 16, 2018

Abell 1033: To Boldly Go into Colliding Galaxy Clusters

Abell 1033
Credit: X-ray: NASA/CXC/Leiden Univ./F. de Gasperin et al;  Optical: SDSS; Radio: LOFAR/ASTRON, NCRA/TIFR/GMRT



Enterprise NCC 1701 USS Enterprise NCC 1701 
Credit: Smithsonian National Air & Space Museum


Hidden in a distant galaxy cluster collision are wisps of gas resembling the starship Enterprise — an iconic spaceship from the "Star Trek" franchise.

Galaxy clusters — cosmic structures containing hundreds or even thousands of galaxies — are the largest objects in the Universe held together by gravity. Multi-million-degree gas fills the space in between the individual galaxies. The mass of the hot gas is about six times greater than that of all the galaxies combined. This superheated gas is invisible to optical telescopes, but shines brightly in X-rays, so an X-ray telescope like NASA's Chandra X-ray Observatory is required to study it. 

By combining X-rays with other types of light, such as radio waves, a more complete picture of these important cosmic objects can be obtained. A new composite image of the galaxy cluster Abell 1033, including X-rays from Chandra (purple) and radio emission from the Low-Frequency Array (LOFAR) network in the Netherlands (blue), does just that. Optical emission from the Sloan Digital Sky Survey is also shown. The galaxy cluster is located about 1.6 billion light years from Earth. 

Using X-ray and radio data, scientists have determined that Abell 1033 is actually two galaxy clusters in the process of colliding. This extraordinarily energetic event, happening from the top to the bottom in the image, has produced turbulence and shock waves, similar to sonic booms produced by a plane moving faster than the speed of sound.

In Abell 1033, the collision has interacted with another energetic cosmic process — the production of jets of high-speed particles by matter spiraling into a supermassive black hole, in this case one located in a galaxy in one of the clusters. These jets are revealed by radio emission to the left and right sides of the image. The radio emission is produced by electrons spiraling around magnetic field lines, a process called synchrotron emission.

The electrons in the jets are traveling at very close to the speed of light. As the galaxy and its black hole moved toward the lower part of the image, the jet on the right slowed down as it crashed into hot gas in the other galaxy cluster. The jet on the left did not slow down because it encountered much less hot gas, giving a warped appearance for the jets, rather than the straight line that is typically seen.

This image of Abell 1033 also provides an example of "pareidolia", a psychological phenomenon where familiar shapes and patterns are seen in otherwise random data. In Abell 1033, the structures in the data create an uncanny resemblance to many of the depictions of the fictional Starship Enterprise from Star Trek.

In terms of astrophysical research, a detailed study of the image shows that the energy of the electrons in the "saucer section" and neck of the starship-shaped radio emission in Abell 1033 is higher than that found in the stardrive section towards the lower left (see labels). This suggests that the electrons have been reenergized, presumably when the jets interact with turbulence or shock waves in the hot gas. The energetic electrons producing the radio emission will normally lose substantial amounts of energy over tens to hundreds of millions of years as they radiate. The radio emission would then become undetectable. However, the vastly extended radio emission observed in Abell 1033, extending over about 500,000 light years, implies that energetic electrons are present in larger quantities and with higher energies than previously thought. One idea is that the electrons have been given a further boost in energy by extra bouts of shocks and turbulence.

Other sources of radio emission in the image besides the starship-shaped object are the shorter jets from another galaxy (labeled "short jets") and a "radio phoenix" consisting of a cloud of electrons that faded in radio emission but was then reenergized when shock waves compressed the cloud. This caused the cloud to once again shine at radio frequencies, as we reported back in 2015.

The team who made this study will use observations with Chandra and LOFAR to look for further examples of colliding galaxy clusters with warped radio emission, to further their understanding of these energetic objects.


A paper describing this result was published in the October 4th, 2017 issue of Science Advances and is available online. The authors of the paper are Francesco de Gasperin, Huib Intema, Timothy Shimwell (Leiden University, the Netherlands), Gianfranco Brunetti (Institute of Radio Astronomy, Italy), Marcus Bruggen (University of Hamburg, Germany), Torsten Enblin (Max Planck Institute for Astrophysics, Germany), Reinout van Weeren (Leiden), Annalisa Bonafede (Hamburg), and Huub Rottgering (Leiden). 

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.


Fast Facts for Abell 1033:

Scale: Image is about 7.4 arcmin across (about 3.3 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 10h 31m 33.70s | Dec +35° 04´ 33.96"
Constellation: Leo Minor
Observation Date: 19 and 21 Feb 2013
Observation Time: 17 hours 35 min
Obs. ID: 15084, 15614
Instrument: ACIS
References: de Gasperin, F et al., Sci. Adv. 2017, 3, 1701634; arXiv:1710.06796
Color Code: X-ray (Pink); Optical (Red, Green, Blue); Radio (Blue)
Distance Estimate: About 1.62 billion light years (z=0.1259)




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Thursday, November 15, 2018

Super-Earth Orbiting Barnard’s Star

Artist’s impression of the surface of a super-Earth orbiting Barnard’s Star

Artist’s impression of super-Earth orbiting Barnard’s Star

Barnard’s Star in the constellation Ophiuchus

Widefield image of the sky around Barnard’s Star showing its motion

Videos

ESOcast 184 Light: Super-Earth Orbiting Barnard’s Star (4K UHD)
ESOcast 184 Light: Super-Earth Orbiting Barnard’s Star (4K UHD)

Artist’s impression of Barnard’s Star and its super-Earth
Artist’s impression of Barnard’s Star and its super-Earth

Exploring the surface of a super-Earth orbiting Barnard’s Star (Artist’s impression)
Exploring the surface of a super-Earth orbiting Barnard’s Star (Artist’s impression)

Barnard’s Star in the Solar neighborhood
Barnard’s Star in the Solar neighborhood


Red Dots campaign uncovers compelling evidence of exoplanet around closest single star to Sun

The nearest single star to the Sun hosts an exoplanet at least 3.2 times as massive as Earth — a so-called super-Earth. One of the largest observing campaigns to date using data from a world-wide array of telescopes, including ESO’s planet-hunting HARPS instrument, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known exoplanet to the Earth. Barnard’s star is the fastest moving star in the night sky.

A planet has been detected orbiting Barnard’s Star, a mere 6 light-years away. This breakthrough — announced in a paper published today in the journal Nature — is a result of the Red Dots and CARMENES projects, whose search for local rocky planets has already uncovered a new world orbiting our nearest neighbour, Proxima Centauri.

The planet, designated Barnard's Star b, now steps in as the second-closest known exoplanet to Earth [1]. The gathered data indicate that the planet could be a super-Earth, having a mass at least 3.2 times that of the Earth, which orbits its host star in roughly 233 days. Barnard’s Star, the planet’s host star, is a red dwarf, a cool, low-mass star, which only dimly illuminates this newly-discovered world. Light from Barnard’s Star provides its planet with only 2% of the energy the Earth receives from the Sun.

Despite being relatively close to its parent star — at a distance only 0.4 times that between Earth and the Sun — the exoplanet lies close to the snow line, the region where volatile compounds such as water can condense into solid ice. This freezing, shadowy world could have a temperature of –170 ℃, making it inhospitable for life as we know it.

Named for astronomer E. E. Barnard, Barnard’s Star is the closest single star to the Sun. While the star itself is ancient — probably twice the age of our Sun — and relatively inactive, it also has the fastest apparent motion of any star in the night sky [2]. Super-Earths are the most common type of planet to form around low-mass stars such as Barnard’s Star, lending credibility to this newly discovered planetary candidate. Furthermore, current theories of planetary formation predict that the snow line is the ideal location for such planets to form.

Previous searches for a planet around Barnard’s Star have had disappointing results — this recent breakthrough was possible only by combining measurements from several high-precision instruments mounted on telescopes all over the world [3].

“After a very careful analysis, we are 99% confident that the planet is there,” stated the team’s lead scientist, Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain). “However, we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.”

Among the instruments used were ESO’s famous planet-hunting HARPS and UVES spectrographs. “HARPS played a vital part in this project. We combined archival data from other teams with new, overlapping, measurements of Barnard’s star from different facilities,” commented Guillem Anglada Escudé (Queen Mary University of London), co-lead scientist of the team behind this result [4]. “The combination of instruments was key to allowing us to cross-check our result.”

The astronomers used the Doppler effect to find the exoplanet candidate. While the planet orbits the star, its gravitational pull causes the star to wobble. When the star moves away from the Earth, its spectrum redshifts; that is, it moves towards longer wavelengths. Similarly, starlight is shifted towards shorter, bluer, wavelengths when the star moves towards Earth.

Astronomers take advantage of this effect to measure the changes in a star’s velocity due to an orbiting exoplanet — with astounding accuracy. HARPS can detect changes in the star’s velocity as small as 3.5 km/h — about walking pace. This approach to exoplanet hunting is known as the radial velocity method, and has never before been used to detect a similar super-Earth type exoplanet in such a large orbit around its star.

“We used observations from seven different instruments, spanning 20 years of measurements, making this one of the largest and most extensive datasets ever used for precise radial velocity studies.” explained Ribas. ”The combination of all data led to a total of 771 measurements — a huge amount of information!”

“We have all worked very hard on this breakthrough,” concluded Anglada-Escudé. “This discovery is the result of a large collaboration organised in the context of the Red Dots project, that included contributions from teams all over the world.


Notes

[1] The only stars closer to the Sun make up the triple star system Alpha Centauri. In 2016, astronomers using ESO telescopes and other facilities found clear evidence of a planet orbiting the closest star to Earth in this system, Proxima Centauri. That planet lies just over 4 light-years from Earth, and was discovered by a team led by Guillem Anglada Escudé.

[2] The total velocity of Barnard’s Star with respect to the Sun is about 500 000 km/h. Despite this blistering pace, it is not the fastest known star. What makes the star’s motion noteworthy is how fast it appears to move across the night sky as seen from the Earth, known as its apparent motion. Barnard’s Star travels a distance equivalent to the Moon's diameter across the sky every 180 years — while this may not seem like much, it is by far the fastest apparent motion of any star.

[3] The facilities used in this research were: HARPS at the ESO 3.6-metre telescope; UVES at the ESO VLT; HARPS-N at the Telescopio Nazionale Galileo; HIRES at the Keck 10-metre telescope; PFS at the Carnegie’s Magellan 6.5-m telescope; APF at the 2.4-m telescope at Lick Observatory; and CARMENES at the Calar Alto Observatory. Additionally, observations were made with the 90-cm telescope at the Sierra Nevada Observatory, the 40-cm robotic telescope at the SPACEOBS observatory, and the 80-cm Joan Oró Telescope of the Montsec Astronomical Observatory (OAdM).

[4] The story behind this discovery will be explored in more detail in this week’s ESOBlog.


More Information

This research was presented in the paper A super-Earth planet candidate orbiting at the snow-line of Barnard’s star published in the journal Nature on 15 November.

The team was composed of I. Ribas (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), M. Tuomi (Centre for Astrophysics Research, University of Hertfordshire, United Kingdom), A. Reiners (Institut für Astrophysik Göttingen, Germany), R. P. Butler (Department of Terrestrial Magnetism, Carnegie Institution for Science, USA), J. C. Morales (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), M. Perger (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), S. Dreizler (Institut für Astrophysik Göttingen, Germany), C. Rodríguez-López (Instituto de Astrofísica de Andalucía, Spain), J. I. González Hernández (Instituto de Astrofísica de Canarias Spain & Universidad de La Laguna, Spain), A. Rosich (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), F. Feng (Centre for Astrophysics Research, University of Hertfordshire, United Kingdom), T. Trifonov (Max-Planck-Institut für Astronomie, Germany), S. S. Vogt (Lick Observatory, University of California, USA), J. A. Caballero (Centro de Astrobiología, CSIC-INTA, Spain), A. Hatzes (Thüringer Landessternwarte, Germany), E. Herrero (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), S. V. Jeffers (Institut für Astrophysik Göttingen, Germany), M. Lafarga (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), F. Murgas (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), R. P. Nelson (School of Physics and Astronomy, Queen Mary University of London, United Kingdom), E. Rodríguez (Instituto de Astrofísica de Andalucía, Spain), J. B. P. Strachan (School of Physics and Astronomy, Queen Mary University of London, United Kingdom), L. Tal-Or (Institut für Astrophysik Göttingen, Germany & School of Geosciences, Tel-Aviv University, Israel), J. Teske (Department of Terrestrial Magnetism, Carnegie Institution for Science, USA & Hubble Fellow), B. Toledo-Padrón (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), M. Zechmeister (Institut für Astrophysik Göttingen, Germany), A. Quirrenbach (Landessternwarte, Universität Heidelberg, Germany), P. J. Amado (Instituto de Astrofísica de Andalucía, Spain), M. Azzaro (Centro Astronómico Hispano-Alemán, Spain), V. J. S. Béjar (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), J. R. Barnes (School of Physical Sciences, The Open University, United Kingdom), Z. M. Berdiñas (Departamento de Astronomía, Universidad de Chile), J. Burt (Kavli Institute, Massachusetts Institute of Technology, USA), G. Coleman (Physikalisches Institut, Universität Bern, Switzerland), M. Cortés-Contreras (Centro de Astrobiología, CSIC-INTA, Spain), J. Crane (The Observatories, Carnegie Institution for Science, USA), S. G. Engle (Department of Astrophysics & Planetary Science, Villanova University, USA), E. F. Guinan (Department of Astrophysics & Planetary Science, Villanova University, USA), C. A. Haswell (School of Physical Sciences, The Open University, United Kingdom), Th. Henning (Max-Planck-Institut für Astronomie, Germany), B. Holden (Lick Observatory, University of California, USA), J. Jenkins (Departamento de Astronomía, Universidad de Chile), H. R. A. Jones (Centre for Astrophysics Research, University of Hertfordshire, United Kingdom), A. Kaminski (Landessternwarte, Universität Heidelberg, Germany), M. Kiraga (Warsaw University Observatory, Poland), M. Kürster (Max-Planck-Institut für Astronomie, Germany), M. H. Lee (Department of Earth Sciences and Department of Physics, The University of Hong Kong), M. J. López-González (Instituto de Astrofísica de Andalucía, Spain), D. Montes (Dep. de Física de la Tierra Astronomía y Astrofísica & Unidad de Física de Partículas y del Cosmos de la Universidad Complutense de Madrid, Spain), J. Morin (Laboratoire Univers et Particules de Montpellier, Université de Montpellier, France), A. Ofir (Department of Earth and Planetary Sciences, Weizmann Institute of Science. Israel), E. Pallé (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), R. Rebolo (Instituto de Astrofísica de Canarias, Spain, & Consejo Superior de Investigaciones Científicas & Universidad de La Laguna, Spain), S. Reffert (Landessternwarte, Universität Heidelberg, Germany), A. Schweitzer (Hamburger Sternwarte, Universität Hamburg, Germany), W. Seifert (Landessternwarte, Universität Heidelberg, Germany), S. A. Shectman (The Observatories, Carnegie Institution for Science, USA), D. Staab (School of Physical Sciences, The Open University, United Kingdom), R. A. Street (Las Cumbres Observatory Global Telescope Network, USA), A. Suárez Mascareño (Observatoire Astronomique de l'Université de Genève, Switzerland & Instituto de Astrofísica de Canarias Spain), Y. Tsapras (Zentrum für Astronomie der Universität Heidelberg, Germany), S. X. Wang (Department of Terrestrial Magnetism, Carnegie Institution for Science, USA), and G. Anglada-Escudé (School of Physics and Astronomy, Queen Mary University of London, United Kingdom & Instituto de Astrofísica de Andalucía, Spain).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.


Links


Contact

 Ignasi Ribas (Lead Scientist)
Institut d’Estudis Espacials de Catalunya and the Institute of Space Sciences, CSIC
Barcelona, Spain
Tel: +34 93 737 97 88 (ext 933027)
Email: iribas@ice.cat

Guillem Anglada-Escudé
Queen Mary University of London
London, United Kingdom
Tel: +44 (0)20 7882 3002
Email: g.anglada@qmul.ac.uk

Calum Turner
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 1537 3591
Email: pio@eso.org

Source: ESO/News

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Wednesday, November 14, 2018

NASA’s Webb Telescope Will Investigate Cosmic Jets From Young Stars

A pair of jets protrude outwards in this infrared image of Herbig-Haro 212 (HH 212), taken by the European Southern Observatory’s Very Large Telescope. Webb’s high resolution and sensitivity will allow astronomers to examine objects like this in greater detail than ever before. Credits: ESO/M. McCaughrean

The formation of a star sounds like a simple process: a cloud of gas collapses in on itself, growing denser and hotter until nuclear fusion ignites and a star begins to shine. The reality is more complex and dramatic.

Swirling gas spins faster and faster, threatening to rip the still-forming star into pieces. Clumps of matter are captured within a tangle of magnetic fields and squirt outward at supersonic speeds. All of it happens within a dusty shroud that blocks visible light. NASA’s James Webb Space Telescope will penetrate that dusty veil and reveal new secrets of star birth.

As an interstellar gas cloud contracts, it spins more rapidly, just as a twirling ice skater does when she draws in her arms. The only way for the gas to continue moving inward is for some of the spin (known as angular momentum) to be removed.

In a process that’s still not fully understood, magnetic fields funnel some of the swirling material into twin jets that shoot outward in opposite directions. These jets travel at speeds of hundreds of miles per second and spread across light-years of space.

“Jets are signposts of star formation,” said Tom Ray, an astronomer at the Dublin Institute for Advanced Studies. Ray and many other scientists are planning to use Webb to study these jets and stellar outflows. Their goals include learning more about how stars form, and how their jets interact with the surrounding interstellar medium of gas and dust.
Over the span of 14 years, the Hubble Space Telescope looked at a bright, clumpy jet known as HH 34 ejected from a young star. Several bright regions in the clumps signify where material is slamming into each other, heating up, and glowing. Credits: NASA, ESA, P. Hartigan (Rice University), and G. Bacon (STScI)

Shock Waves in Space

They will study objects like Herbig-Haro (HH) 212, located about 1,400 light-years away in the constellation Orion. At the center of HH 212 resides a still-forming star or protostar that will eventually grow to become about the mass of our Sun. Jets from the protostar extend across about 5 light-years of space.

The material in those jets is traveling at supersonic speeds. When it slams into surrounding material, it creates a shock wave, much like the “sonic boom” of a supersonic aircraft. The shock heats the interstellar gas, causing it to glow at specific wavelengths of light that depend on the conditions within the shock wave itself.

“With Webb, we’ll be able to dissect the interactions of the protostar with its surroundings that were previously blurred into a single blob,” said Ewine van Dishoeck of Leiden University.

Webb’s exquisite angular resolution will allow it to pick up the tiniest details. This will allow it to see solar-system-scale features at the distance of objects like HH 212. And since the farther along a jet you go from the protostar, the longer the time since the material was ejected, astronomers can probe the history of the star’s matter-gathering or accretion process.

“Webb has higher sensitivity and higher angular resolution at long infrared wavelengths than anything we could do previously. Webb will answer questions we can’t answer from the ground,” said Alberto Noriega-Crespo of the Space Telescope Science Institute.

Webb also will precisely discern different wavelengths of infrared light. This will allow it to detect infrared light from a variety of chemical elements associated with the shock wave, including iron, neon and sulfur.

When a jet of material traveling at supersonic speeds slam into interstellar gas and dust, it creates a shock wave that compresses and heats matter.  Credits: NASA and J. Olmsted (STScI). Hi-res image

A New Star Emerges

HH 212 is about 100,000 years old. Over the course of the next million years, its protostar will gather a sun’s worth of gas. The remainder of the surrounding material will either condense into planets or get swept away by outflows and other processes. Eventually, a fully formed star will emerge.

“By studying HH 212, and objects like it, we want to learn how jets and outflows help the star escape from its cocoon,” said Mark McCaughrean of the European Space Agency.

The observations described here will be taken as part of Webb’s Guaranteed Time Observation (GTO) program. The GTO program provides dedicated time to the scientists who have worked with NASA to craft the science and instrument capabilities of Webb throughout its development.

The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries of 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 project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency.

For more information about Webb, visit www.nasa.gov/webb

By Christine Pulliam
Space Telescope Science Institute, Baltimore, Md.

 Editor: Lynn Jenner


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Friday, November 09, 2018

Tiny Old Star Has Huge Impact

The newly discovered star system orbits the galaxy on a circular orbit that, like the orbit of the Sun, never gets too far from the plane of the galaxy. On the other hand, most ultra metal-poor stars have orbits that take them across the galaxy and far from its plane. Credit: Kevin Schlaufman.

The new discovery is only 14% the size of the Sun and is the new record holder for the star with the smallest complement of heavy elements. It has about the same heavy element proportion as Mercury, the smallest planet in our solar system. Credit: Kevin Schlaufman. Full resolution JPG

Astronomers use the Gemini Observatory to investigate a tiny star that is likely the oldest known star in the disk of our galaxy. The diminutive star could have a disproportionate impact on our understanding of the age and history of our Milky Way Galaxy. It also provides a unique glimpse into the conditions present in the young Universe shortly after the Big Bang.

A tiny star found in our galactic neighborhood is presenting astronomers with a compelling glimpse into the history of our galaxy and the early Universe. The star has some very interesting characteristics: it’s small, it’s old, and most significantly it’s made of material very similar to that spewed by the Big Bang. To host a star like this suggests that the disk of our galaxy could be up to three billion years older than previously thought.

“Our Sun likely descended from thousands of generations of short-lived massive stars that have lived and died since the Big Bang,” said Kevin Schlaufman of Johns Hopkins University, leader of this study published in the November 5th issue of The Astrophysical Journal. “However, what’s most interesting about this star is that it had perhaps only one ancestor separating it and the beginnings of everything,” Schlaufman adds.

The Big Bang theory dates our Universe at about 13.7 billion years and suggests that the first stars were made almost exclusively of hydrogen and helium. As stars die and gradually recycle their materials into new stars, heavier elements formed. Astronomers refer to stars which lack heavier elements as low metallicity stars. “But this one has such low metallicity,” said Schlaufman, “it’s known as an ultra metal poor star – this star may be one in ten million.

” The star, which goes by the designation 2MASS J18082002-5104378 B, also challenges the assumption that the first stars in the Universe were large, exclusively high-mass and short-lived stars. In addition, its location within the usually active and crowded disk of our galaxy is unexpected.

2MASS J18082002–5104378 B is a part of a binary star system. It is the smaller companion to a larger low-metallicity star observed in 2014 and 2015 by the European Southern Observatory's Very Large Telescope UT2. Before the discovery of the tiny star, astronomers mistakenly believed that this binary system might contain a black hole or neutron star. From April 2016 to July 2017, Schlaufman and his team used both the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope in Chile and the Magellan Clay Telescope at Las Campanas Observatory to dissect the star system’s light and measure the object’s relative motions, thus discovering the tiny star by detecting its gravitational tug on its partner.

"Gemini was critical to this discovery, as its flexible observing modes enabled weekly check-ins on the system over six months," Schlaufman confirms.

“Understanding the history of our own galaxy is critical for humanity to understand the broader history of the entire Universe,” said Chris Davis of the United State’s National Science Foundation (NSF). NSF funds the Gemini Observatory on behalf of the United States, additional international partners are listed at the end of this release.

2MASS J18082002–5104378 B has only about 14% the mass of our Sun making it a red dwarf star. While average-sized stars like our Sun live for approximately 10 billion years before extinguishing their nuclear fuel, low-mass stars can burn for trillions of years.

“Diminutive stars like these tend to shine for a very long time,” said Schlaufman. “This star has aged well. It looks exactly the same today as it did when it formed 13.5 billion years ago.”

The discovery of 2MASS J18082002–5104378 B gives astronomers hope for finding more of these old stars which provide a glimpse at the very early Universe. Only about 30 ultra metal poor stars have been identified. “Observations such as these are paving the way to perhaps one day finding that ever elusive first generation star,” concludes Schlaufman.


Johns Hopkins University news release

Media Contacts:

 Peter Michaud
Public Information and Outreach manager
Gemini Observatory
Email: pmichaud@gemini.edu
Phone: 808-974-2510
Cell: 808-936-6643

 Jill Rosen
Senior Media Relations Representative
Johns Hopkins University
Email: jrosen@jhu.edu
Desk: 443-997-9906
Cell: 443-547-8805

 Science Contact:

 Kevin Schlaufman
Assistant Professor of Physics and Astronomy
Johns Hopkins University
Email: kschlaufman@jhu.edu
Office Phone: 410-516-3295
Cell Phone: 814-490-9177



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Thursday, November 08, 2018

Astronomers Unveil Growing Black Holes in Colliding Galaxies

Galaxy Mergers 
NASA, ESA, and M. Koss (Eureka Scientific, Inc.); Hubble image: NASA, ESA, and M. Koss (Eureka Scientific, Inc.); Keck images: W. M. Keck Observatory and M. Koss (Eureka Scientific, Inc.); Pan-STARRS images: Panoramic Survey Telescope and Rapid Response System and M. Koss (Eureka Scientific, Inc.). Release images


Peering through thick walls of gas and dust surrounding the messy cores of merging galaxies, astronomers are getting their best view yet of close pairs of supermassive black holes as they march toward coalescence into mega black holes.

A team of researchers led by Michael Koss of Eureka Scientific Inc., in Kirkland, Washington, performed the largest survey of the cores of nearby galaxies in near-infrared light, using high-resolution images taken by NASA's Hubble Space Telescope and the W. M. Keck Observatory in Hawaii. The Hubble observations represent over 20 years' worth of snapshots from its vast archive.

"Seeing the pairs of merging galaxy nuclei associated with these huge black holes so close together was pretty amazing," Koss said. "In our study, we see two galaxy nuclei right when the images were taken. You can't argue with it; it's a very 'clean' result, which doesn't rely on interpretation."

The images also provide a close-up preview of a phenomenon that must have been more common in the early universe, when galaxy mergers were more frequent. When galaxies collide, their monster black holes can unleash powerful energy in the form of gravitational waves, the kind of ripples in space-time that were just recently detected by ground-breaking experiments.

The new study also offers a preview of what will likely happen in our own cosmic backyard, in several billion years, when our Milky Way combines with the neighboring Andromeda galaxy and their respective central black holes smash together.

"Computer simulations of galaxy smashups show us that black holes grow fastest during the final stages of mergers, near the time when the black holes interact, and that's what we have found in our survey," said study team member Laura Blecha of the University of Florida, in Gainesville. "The fact that black holes grow faster and faster as mergers progress tells us galaxy encounters are really important for our understanding of how these objects got to be so monstrously big."

A galaxy merger is a slow process lasting more than a billion years as two galaxies, under the inexorable pull of gravity, dance toward each other before finally joining together. Simulations reveal that galaxies kick up plenty of gas and dust as they undergo this slow-motion train wreck.

The ejected material often forms a thick curtain around the centers of the coalescing galaxies, shielding them from view in visible light. Some of the material also falls onto the black holes at the cores of the merging galaxies. The black holes grow at a fast clip as they engorge themselves with their cosmic food, and, being messy eaters, they cause the infalling gas to blaze brightly. This speedy growth occurs during the last 10 million to 20 million years of the union. The Hubble and Keck Observatory images captured close-up views of this final stage, when the bulked-up black holes are only about 3,000 light-years apart — a near-embrace in cosmic terms.

It's not easy to find galaxy nuclei so close together. Most prior observations of colliding galaxies have caught the coalescing black holes at earlier stages when they were about 10 times farther away. The late stage of the merger process is so elusive because the interacting galaxies are encased in dense dust and gas and require high-resolution observations in infrared light that can see through the clouds and pinpoint the locations of the two merging nuclei.

The team first searched for visually obscured, active black holes by sifting through 10 years' worth of X-ray data from the Burst Alert Telescope (BAT) aboard NASA's Neil Gehrels Swift Telescope, a high-energy space observatory. "Gas falling onto the black holes emits X-rays, and the brightness of the X-rays tells you how quickly the black hole is growing," Koss explained. "I didn't know if we would find hidden mergers, but we suspected, based on computer simulations, that they would be in heavily shrouded galaxies.Therefore we tried to peer through the dust with the sharpest images possible, in hopes of finding coalescing black holes."

The researchers combed through the Hubble archive, identifying those merging galaxies they spotted in the X-ray data. They then used the Keck Observatory's super-sharp, near-infrared vision to observe a larger sample of the X-ray-producing black holes not found in the Hubble archive.

"People had conducted studies to look for these close interacting black holes before, but what really enabled this particular study were the X-rays that can break through the cocoon of dust," Koss said. "We also looked a bit farther in the universe so that we could survey a larger volume of space, giving us a greater chance of finding more luminous, rapidly growing black holes."

The team targeted galaxies with an average distance of 330 million light-years from Earth. Many of the galaxies are similar in size to the Milky Way and Andromeda galaxies. The team analyzed 96 galaxies from the Keck Observatory and 385 galaxies from the Hubble archive found in 38 different Hubble observation programs. The sample galaxies are representative of what astronomers would find by conducting an all-sky survey.

To verify their results, Koss's team compared the survey galaxies with 176 other galaxies from the Hubble archive that lack actively growing black holes. The comparison confirmed that the luminous cores found in the researchers' census of dusty interacting galaxies are indeed a signature of rapidly growing black-hole pairs headed for a collision.

When the two supermassive black holes in each of these systems finally come together in millions of years, their encounters will produce strong gravitational waves. Gravitational waves produced by the collision of two stellar-mass black holes have already been detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). Observatories such as the planned NASA/ESA space-based Laser Interferometer Space Antenna (LISA) will be able to detect the lower-frequency gravitational waves from supermassive black-hole mergers, which are a million times more massive than those detected by LIGO.

Future infrared telescopes, such as NASA's planned James Webb Space Telescope and a new generation of giant ground-based telescopes, will provide an even better probe of dusty galaxy collisions by measuring the masses, growth rate, and dynamics of close black-hole pairs. The Webb telescope may also be able to look in mid-infrared light to uncover more galaxy interactions so encased in thick gas and dust that even near-infrared light cannot penetrate them.

The team's results will appear online in the Nov. 7, 2018, issue of the journal Nature.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). 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.


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Contact

 Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Michael Koss
Eureka Scientific Inc., Kirkland, Washington
Michael.Koss@eurekasci.com


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Wednesday, November 07, 2018

Cosmic Collisions: SOFIA Unravels the Mysterious Formation of Star Clusters

Illustration of a star cluster forming from the collision of turbulent molecular clouds, which appear as dark shadows in front of the background galactic star field.Credits: NASA/SOFIA/Lynette Cook. Hi-res image

Illustration of the molecular clouds surrounded by atomic envelopes, in green, which have been detected by SOFIA via emission from ionized carbon. The spatial offset and motions of these envelopes confirm predictions of simulations of cloud collisions.Credits: NASA/SOFIA/Lynette Cook. Hi-res image


The sun, like all stars, was born in a giant cold cloud of molecular gas and dust. It may have had dozens or even hundreds of stellar siblings – a star cluster – but these early companions are now scattered throughout our Milky Way galaxy. Although the remnants of this particular creation event have long since dispersed, the process of star birth continues today within our galaxy and beyond. Star clusters are conceived in the hearts of optically dark clouds where the early phases of formation have historically been hidden from view. But these cold, dusty clouds shine brightly in the infrared, so telescopes like the Stratospheric Observatory for Infrared Astronomy, SOFIA, can begin to reveal these long-held secrets. 

Traditional models claim that the force of gravity may be solely responsible for the formation of stars and star clusters. More recent observations suggest that magnetic fields, turbulence, or both are also involved and may even dominate the creation process. But just what triggers the events that lead to the formation of star clusters?

Astronomers using SOFIA’s instrument, the German Receiver for Astronomy at Terahertz Frequencies, known as GREAT, have found new evidence that star clusters form through collisions between giant molecular clouds.

The results were published in the Monthly Notices of the Royal Astronomical Society.

"Stars are powered by nuclear reactions that create new chemical elements," said Thomas Bisbas, a postdoctoral researcher at the University of Virginia, Charlottesville, Virginia, and the lead author on the paper describing these new results. "The very existence of life on earth is the product of a star that exploded billions of years ago, but we still don't know how these stars — including our own sun — form."

Researchers studied the distribution and motion of ionized carbon around a molecular cloud where stars can form. There appear to be two distinct components of molecular gas colliding with each other at speeds of more than 20,000 miles per hour. The distribution and velocity of the molecular and ionized gases are consistent with simulations of cloud collisions, which indicate that star clusters form as the gas is compressed in the shock wave created as the clouds collide.

“These star formation models are difficult to assess observationally,” said Jonathan Tan, a professor at Chalmers University of Technology in Gothenburg, Sweden, and the University of Virginia, and a lead researcher on the paper. “We’re at a fascinating point in the project, where the data we are getting with SOFIA can really test the simulations.”

While there is not yet scientific consensus on the mechanism responsible for driving the creation of star clusters, these SOFIA observations have helped scientists take an important step toward unraveling the mystery. This field of research remains an active one, and these data provide crucial evidence in favor of the collision model. The authors expect future observations will test this scenario to determine if the process of cloud collisions is unique to this region, more widespread, or even a universal mechanism for the formation of star clusters.

“Our next step is to use SOFIA to observe a larger number of molecular clouds that are forming star clusters,” added Tan. “Only then can we understand how common cloud collisions are for triggering star birth in our galaxy.”

SOFIA is a Boeing 747SP jetliner modified to carry a 106-inch diameter telescope. It is a joint project of NASA and the German Aerospace Center, DLR. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science and mission operations in cooperation with the Universities Space Research Association headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart. The aircraft is maintained and operated from NASA’s Armstrong Flight Research Center Hangar 703, in Palmdale, California.

Media Point of Contact

Nicholas A. Veronico
Nicholas.A.Veronico@nasa.gov • SOFIA Science Center
NASA Ames Research Center, Moffett Field, California

Editor: Kassandra Bell

Source:  NASA/Stars

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