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Stellar News Feed Archive

Surprising Theorists, Stars Within Middle-Aged Clusters Are of Similar Age Wednesday, December 17, 2014 - 18:19

“NGC 1651 is the best example found to date of a truly single-age stellar population,” said Richard de Grijs, a faculty member at KIAA involved in the study. “We have since identified a handful of other middle-aged clusters that appear to show similar features.”

The research suggests that, for middle-aged clusters at least, today’s conventional wisdom may be wrong and it might be common for all stars in a single cluster to be of approximately the same age.

A decade ago, astronomers actually thought that the stars within any cluster should all be about the same age, but that idea fell out of favor when clear evidence of the presence of stars of different ages within a single cluster was discovered, at least for the oldest and most populous clusters in our Milky Way. Based on today’s Nature paper, a reverse shift looks necessary.

Read the full story from the Kavli Foundation

 

Characterizing Cepheid Light Curves Tuesday, December 16, 2014 - 19:12

Measuring the mean magnitude or period of a Cepheid, however, can be a pretty demanding task in its own right. A Cepheid’s light curve looks different in different wavelengths (as shown in Figure 1, taken from Madore and Freedman 1991). The shorter-wavelength bands like the B and V-bands have light curves with larger amplitudes of variation and more asymmetry than the light curves in longer-wavelength near-infrared bands like J, H, and K. This makes it easier to detect and characterize the Cepheids in the B and V bands, but harder to accurately determine the mean magnitude of a Cepheid in those wavelengths, since we have to know accurately what phase of the light curve we are observing in order to get a good measurement of the mean magnitude. In practice, we often want to use measure the periods using light curves from shorter wavelengths and measure the mean magnitudes using light curves from longer wavelengths.

Read the full summary on Astrobites

Read the paper "New NIR light-curve templates for classical Cepheids" on astro-ph

 

The occurrence of classical Cepheids in binary systems Thursday, December 11, 2014 - 21:42

Classical Cepheids, like binary stars, are laboratories for stellar evolution and Cepheids in binary systems are especially powerful ones. About one-third of Galactic Cepheids are known to have companions and Cepheids in eclipsing binary systems have recently been discovered in the Large Magellanic Cloud. However, there are no known Galactic binary Cepheids with orbital periods less than one year. We compute population synthesis models of binary Cepheids to compare to the observed period and eccentricity distributions of Galactic Cepheids as well as to the number of observed eclipsing binary Cepheids in the LMC. We find that our population synthesis models are consistent with observed binary properties of Cepheids. Furthermore, we show that binary interaction on the red giant branch prevents some red giant stars from becoming classical Cepheids. Such interactions suggest that the binary fraction of Cepheids should be significantly less than that of their main-sequence progenitors, and that almost all binary Cepheids have orbital periods longer than one year. If the Galactic Cepheid spectroscopic binary fraction is about 35%, then the spectroscopic binary fraction of their intermediate mass main sequence progenitors is about 40-45%.

Authors: Hilding R. Neilson, Fabian R.N. Schneider, Robert G. Izzard, Nancy R. Evans, Norbert Langer

Read the paper on astro-ph

 

Astronomers observe two stars so close to each other that they will end up merging into a supermassive star Monday, December 8, 2014 - 15:27

This article concludes that MY Cam is the most massive binary star observed and its components, two stars of spectral type O (blue, very hot and bright), 38 and 32 times the Sun's mass, are still on the main sequence and are very close to each other, with an orbital period of less than 1.2 days, in other words, the shortest orbital period in this type of stars. This indicates that the binary was virtually formed as it is now: the stars were almost in contact at the time they were formed.

The expected development is the merger of both components into a single object over 60 solar masses before any of them have time to evolve significantly. Hence, these results demonstrate the viability of some theoretical models suggesting that most massive stars are formed by merging less massive stars.

Read the article (English)

Read the article (Spanish)

Read the paper "MY Camelopardalis, a very massive merger progenitor" on astro-ph

 

Twinkle, Twinkle New-Born Star Sunday, December 7, 2014 - 20:34

Stars are born in dense, cool clouds of molecular gas and dust. When the local density is high enough, the matter can gravitationally collapse to form a new star, a so-called young stellar object (YSO). In its early phases, a thick envelope dominates the infrared emission from the YSO, hiding what is going on within, but eventually the envelope flattens out into a warm circumstellar accretion disk. The disk emits more infrared than does the young star, and that excess radiation can be used to distinguish young stars from more mature stars whose disks and envelopes have disappeared. In recent years it has become possible to investigate these envelopes and disks in more detail, and astronomers have been building on these studies to address how planetary systems develop.

Read the story at CfA News

Read the paper on astro-ph

 

Making Order Out of Chaos Wednesday, December 3, 2014 - 12:25

Today’s paper looks at this phenomenon with a telescope that is normally associated with exoplanets—Kepler.  In order to fully understand the chaotic nature of RR Lyrae stars, the authors needed a long, continuous data set and an aperture capable of capturing the full light curve of the stars in question. Kepler is great at the former, but it is designed to search for small dips of light to detect exoplanets. Because of this, the “optimal” apertures used to detect exoplanets cut out a small fraction of the host star’s light. Removing RR Lyrae light, however, would lead to an inaccurate light curve. To complete this study, the authors created larger, specialized aperture masks to capture the full light curve of the RR Lyrae stars.

Read the full paper summary on Astrobites

 

Keck Interferometer Reveals Sun-Like Stars Not All That Dusty Wednesday, December 3, 2014 - 12:18

Planet hunters received some good news recently. A new study concluded that, on average, sun-like stars aren’t all that dusty. Less dust means better odds of snapping clear pictures of the stars’ planets in the future.

These results come from surveying nearly 50 stars from 2008 to 2011 using the Keck Interferometer, a former NASA key science project that combined the power of the twin W. M. Keck Observatory telescopes atop Mauna Kea, Hawaii.

“Dust is a double-edged sword when it comes to imaging distant planets,” explained Bertrand Mennesson of NASA’s Jet Propulsion Laboratory, Pasadena, California, lead author of an Astrophysical Journal report to be published online December 8. “The presence of dust is a signpost for planets, but too much dust can block our view.” 

Read the full story at SciTechDaily

 

A Colourful Gathering of Middle-aged Stars Wednesday, November 26, 2014 - 09:04

This grouping of stars is about 300 million years old. This makes it middle-aged by open star cluster standards. The cluster stars that started off with moderate masses are still shining brightly with blue-white colours, but the more massive ones have already exhausted their supplies of hydrogen fuel and have become red giant stars. As a result the cluster appears rich in both blue and orange stars. The most massive stars in the original cluster will have already run through their brief but brilliant lives and exploded as supernovae long ago. There are also numerous less conspicuous fainter stars of lower mass that have longer lives and shine with yellow or red hues. NGC 3532 consists of around 400 stars in total.

Read the full desxription in the ESO news release

 

Discovery of ZZ Cetis in detached white dwarf plus main-sequence binaries Sunday, November 23, 2014 - 09:15

We present the first results of a dedicated search for pulsating white dwarfs (WDs) in detached white dwarf plus main-sequence binaries. Candidate systems were selected from a catalogue of WD+MS binaries, based on the surface gravities and effective temperatures of the WDs. We observed a total of 26 systems using ULTRACAM mounted on ESO's 3.5m New Technology Telescope (NTT) at La Silla. Our photometric observations reveal pulsations in seven WDs of our sample, including the first pulsating white dwarf with a main-sequence companion in a post common envelope binary, SDSSJ1136+0409. Asteroseismology of these new pulsating systems will provide crucial insight into how binary interactions, particularly the common envelope phase, affect the internal structure and evolution of WDs. In addition, our observations have revealed the partially eclipsing nature of one of our targets, SDSSJ1223-0056.

Authors: S. Pyrzas, B. T. Gaensicke, J. J. Hermes, C. M. Copperwheat, A. Rebassa-Mansergas, V. S. Dhillon, S. P. Littlefair, T. R. Marsh, S. G. Parsons, C. D. J. Savoury, M. R. Schreiber, S. C. C. Barros, J. Bento, E. Breedt, P. Kerry

Read the paper on astro-ph

 

Doppler images of the eclipsing binary ER Vulpeculae Sunday, November 23, 2014 - 09:07

We present Doppler images of both components of the eclipsing binary system ER Vul, based on the spectra obtained in 2004 November, 2006 September and 2008 November. The least-squares deconvolution technique is used for enhancing the signal-to-noise ratios of the observed profiles. The new surface images reveal that both stars of ER Vul show strong starspot activities and the starspots appear at various latitudes. The surface maps of 2006 and 2008 both show the presence of large high-latitude starspots on each component of ER Vul. We find no obvious phase shift of the active regions during our observations. The longitude distributions of starspots are non-uniform on both stars. At low-to-mid latitudes, the active regions are almost exclusively found in the hemisphere facing the other star. However, we find no pronounced concentration of spots at the sub-stellar points.

 

Authors: Yue Xiang, Shenghong Gu, A. Collier Cameron, J. R. Barnes

 

Read the paper on astro-ph

 

Real-Time Stellar Evolution Saturday, November 22, 2014 - 09:38

To get an idea of how stars live and die, we can’t just pick one and watch its life unfold in real time. Most stars live for billions of years! So instead, we do a population census of sorts. Much like you can study how humans age by taking a “snapshot” of individuals ranging from newborn to elderly, so too can we study the lives of stars.

But like all good things in life (and stars), there are exceptions. Sometimes, stellar evolution happens on more human timescales—tens to hundreds of years rather than millions or billions. One such exception is the topic of today’s paper: planetary nebulae, and the rapidly dying stellar corpses responsible for all that glowing gas.

All stars similar to our Sun, or up to about eight times as massive, will end their lives embedded in planetary nebulae like these. The name is a holdover from their discovery and general appearance—we have long known that planetary nebulae have nothing to do with planets. Instead, they are the former outer layers of a star: an envelope of material hastily ejected when gravity can no longer hold a star together. In its final death throes, what’s left of the star rapidly heats up and begins to ionize gas in the nebula surrounding it.

Read the full summary on Astrobites

 

NASA's Swift Mission Probes an Exotic Object: ‘Kicked’ Black Hole or Mega Star? Wednesday, November 19, 2014 - 15:21

An international team of researchers analyzing decades of observations from many facilities, including NASA's Swift satellite, has discovered an unusual source of light in a galaxy some 90 million light-years away.

The object's curious properties make it a good match for a supermassive black hole ejected from its home galaxy after merging with another giant black hole. But astronomers can't yet rule out an alternative possibility. The source, called SDSS1133, may be the remnant of a massive star that erupted for a record period of time before destroying itself in a supernova explosion.

"With the data we have in hand, we can't yet distinguish between these two scenarios," said lead researcher Michael Koss, an astronomer at ETH Zurich, the Swiss Federal Institute of Technology. "One exciting discovery made with NASA's Swift is that the brightness of SDSS1133 has changed little in optical or ultraviolet light for a decade, which is not something typically seen in a young supernova remnant." 

Read the full NASA Swift press release

 

GSC 4560--02157: a New Long-period Eclipsing Cataclysmic Variable Star Tuesday, November 18, 2014 - 10:49

Abstract: We study the newly discovered variable star GSC 4560--02157. CCD photometry was performed in 2013--2014, and a spectrum was obtained with the 6-m telescope in June, 2014. GSC 4560--02157 is demonstrated to be a short-period (P=0.265359d) eclipsing variable star. All its flat-bottom primary minima are approximately at the same brightness level, while the star's out-of-eclipse brightness and brightness at secondary minimum varies considerably (by up to 0.6m) from cycle to cycle. Besides, there are short-term (time scale of 0.03-0.04 days) small-amplitude brightness variations out of eclipse. This behavior suggests cataclysmic nature of the star, confirmed with a spectrum taken on June 5, 2014. The spectrum shows numerous emissions of the hydrogen Balmer series, HeI, HeII.

Authors: A.V. Khruslov, A.V. Kusakin, E.A. Barsukova, V.P. Goranskij, A.F. Valeev, N.N. Samus

Read the paper on astro-ph

 

ASASSN-13co: A Type-Defying Supernova Tuesday, November 18, 2014 - 08:46

There are arguably a lot of things defy categorization, but it’s not everyday that we find something that suggests we do away with our categories altogether. The authors of today’s paper believe that the recently-discovered Type II supernova ASASSN-13co — read that as “assassin”, please — might just be one of the latter. Its unusual characteristics call into question the validity of the two classes (II-P and II-L, more on that later) into which we usually group Type II supernovae. As a result, they suggest that we treat Type II supernovae properties as a continuum, rather than the discrete designations we’ve become accustomed to assigning.

Death Throes of Massive Stars

Type II supernovae are identified by the hydrogen in their spectra (meaning that they still have a hydrogen envelope when they die). They are formed when a star with mass of 8-50 times that of the sun dies through core-collapse.

All stars produce energy through nuclear fusion, but massive stars can fuse much heavier nuclei than stars the size of our sun – all the way to nickel and iron, which have the highest binding energy of all elements. While the fusion of the lighter elements is an exothermic process, fusing iron uses up energy instead, so fusing elements heavier than iron isn’t energetically favorable. As a result, a core of iron and nickel (which then decays into iron) builds up in the center of a massive star. The core is supported by electron degeneracy pressure. When the mass of the iron-nickel core exceeds the Chandrasekhar limit (about 1.4 solar masses), however, electron degeneracy pressure is not enough to stop the core from collapsing. As the core collapses, the protons and electrons in the core of the star merge to form neutrons and neutrinos. The neutrinos can escape and carry away energy. At the same time, the outer layers of the star fall inward until neutrondegeneracy pressure kicks in, stopping the collapse and causing the outer layers to rebound.  The combination of the pressure from the neutrinos and the rebound of the outer layers off of the core causes the star to be torn apart in a huge explosion – a core-collapse supernovae.

Read the article on Astrobites

 

Astrochemical Dating of a Stellar Nursery Monday, November 17, 2014 - 21:33

An international research team led by scientists from the Coordinated Research Center (CRC) 956 “Conditions and Impact of Star Formation” at the University of Cologne has used observations made with the GREAT instrument on board the SOFIA aircraft observatory and the APEX telescope to date the core of an interstellar cloud that is forming a group of Sun-like stars.

The age of this star-forming cloud, which is located in the Ophiuchus constellation at a distance of around 400 light years, was determined by comparing the data from the telescopes with extensive computer simulations of the chemistry that is changing with time. “The simulations allow us a detailed look at the movement of our H2D+ clock,” explains Jorma Harju of the University of Helsinki. “We find that our new chemical clock is more precise than any of those used previously. Even more importantly, it keeps running when other clocks have already stopped working.” The team is confident that their new method will help to date other stellar birthplaces.

Read the press release from Uni­ver­sity of Cologne

 

The Party's Over for These Youthful Compact Galaxies Friday, November 14, 2014 - 10:33

Researchers using NASA's Hubble Space Telescope and Chandra X-ray Observatory have uncovered young, massive, compact galaxies whose raucous star-making parties are ending early. The firestorm of star birth has blasted out most of the remaining gaseous fuel needed to make future generations of stars. Now the party's over for these gas-starved galaxies, and they are on track to possibly becoming so-called "red and dead galaxies," composed only of aging stars.

Astronomers have debated for decades how massive galaxies rapidly evolve from active star-forming machines to star-starved graveyards. Previous observations of these galaxies reveal geysers of gas shooting into space at up to 2 million miles an hour. Astronomers have suspected that powerful monster black holes lurking at the centers of the galaxies triggered the gaseous outflows and shut down star birth by blowing out any remaining fuel.

Now an analysis of 12 merging galaxies at the end of their star-birthing frenzy is showing that the stars themselves are turning out the lights on their own star-making party. This happened when the universe was half its current age of 13.7 billion years.

Read the full HubbleSite press release

 

Primordial galaxy bursts with starry births Wednesday, November 12, 2014 - 16:00

An international team of researchers gazed back over 12.5 billion years to find bustling galaxies creating stars at a breakneck rate. Today, Earth’s Milky Way galaxy produces the equivalent of perhaps two to three new suns a year. The AzTEC-3 galaxy, observed to be emerging from the Big Bang’s primordial soup, creates about 1,100 suns a year, corresponding to about three suns each day.

Lead author Dominik Riechers says that galaxies with this quick rate of star production have been known to exist in the middle-aged universe, say 3 billion to 6 billion years old, but this production is surprising for galaxies in their cosmic infancy. “We expect this out of later galaxies in a more mature universe, but not from one of the earliest,” he said.

Read the press release from Cornell here

Read the paper on astro-ph

 

Intriguing triple-mode RR Lyrae star with period doubling Wednesday, November 12, 2014 - 09:34

We report the discovery of an intriguing triple-mode RR Lyrae star found in the OGLE Galactic bulge collection, OGLE-BLG-RRLYR-24137. In the OGLE catalog the star was identified as RRd star - double-mode pulsator, pulsating simultaneously in the fundamental and in the first overtone modes. We find that third mode is excited and firmly detect its period doubling. Period ratios are not far from that expected for triple-mode - fundamental, first and third overtone - pulsation. Unfortunately, we cannot reproduce period ratios of the three modes with a consistent set of pulsation models. Therefore the other interpretation, that additional mode is non-radial, is also likely.

Authors: R. Smolec, I. Soszyński, A. Udalski, M.K. Szymański, P. Pietrukowicz, J. Skowron, S. Kozłowski, R. Poleski, P. Moskalik, D. Skowron, G. Pietrzyński, Ł. Wyrzykowski, K. Ulaczyk, P. Mróz

Read the paper on astro-ph

 

Birth of Planets Revealed in Astonishing Detail in ALMA’s ‘Best Image Ever’ Thursday, November 6, 2014 - 18:24

Astronomers have captured the best image ever of planet formation around an infant star as part of the testing and verification process for the Atacama Large Millimeter/submillimeter Array’s (ALMA) new high-resolution capabilities. 

This revolutionary new image reveals in astonishing detail the planet-forming disk surrounding HL Tau, a Sun-like star located approximately 450 light-years from Earth in the constellation Taurus.  

ALMA uncovered never-before-seen features in this system, including multiple concentric rings separated by clearly defined gaps. These structures suggest that planet formation is already well underway around this remarkably young star.

"These features are almost certainly the result of young planet-like bodies that are being formed in the disk. This is surprising since HL Tau is no more than a million years old and such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image," said ALMA Deputy Director Stuartt Corder. 

Read the full press release

Jets, bubbles, and bursts of light in Taurus Thursday, November 6, 2014 - 18:21

 

The NASA/ESA Hubble Space Telescope has snapped a striking view of a multiple star system called XZ Tauri, its neighbour HL Tauri, and several nearby young stellar objects. XZ Tauri is blowing a hot bubble of gas into the surrounding space, which is filled with bright and beautiful clumps that are emitting strong winds and jets. These objects illuminate the region, creating a truly dramatic scene.

This dark and ominous landscape is located some 450 light-years away in the constellation of Taurus (The Bull). It lies in the north-eastern part of a large, dark cloud known as LDN 1551.

Just to the left of centre in this image, embedded within a rust-coloured cloud, lies XZ Tauri. While it appears to be a single star, this bright spot actually consists of several stars. It has long been known to be a binary, but one of these two stars is thought also to be a binary, making a total of three stars within a single system.

Read the full press release

 

F stars: A challenge to stellar evolution Monday, November 3, 2014 - 10:50

Many main-sequence F and early G stars are too luminous for their effective temperature, surface gravity, and chemical composition. These  "overluminous stars" have two curious properties. First, their kinematics as a function of age from stellar evolution modeling (isochrone fitting) is very different from that of normal stars. Second, while X-ray luminosity of normal stars declines with age, the X-ray luminosity of overluminous F stars changes in the opposite direction, being on average higher for older stars. These properties imply that, in defiance of standard models of stellar evolution, F stars of a given mass and chemical composition can evolve very differently. Assuming that the models correctly describe normal stars, for overluminous F stars they predict too young age and the X-ray emission evolving in the direction opposite to the actually observed trend. This discrepancy between modeling results and observational data suggests that standard stellar evolution models and models of stellar activity are missing some important factors, which makes stellar age and predictions for stellar activity from these models problematic. The data and literature analysis presented in this paper point to a nonuniform rotation of the stellar interior as a plausible key factor able to reconcile the divergent trends in age-velocity relationships of normal and overluminous F stars and explain in a coherent and self-consistent way the overluminosity phenomenon.

Authors: A. A. Suchkov, S. A. Lyapustina

Read the paper on astro-ph

 

Detection of a Light Echo from the Otherwise Normal SN 2007af Friday, October 31, 2014 - 08:50

We present the discovery of a light echo from SN 2007af, a normal Type Ia supernova (SN Ia)
in NGC 5584. Hubble Space Telescope (HST) images taken three years post explosion reveal two
separate echoes; an outer echo and extended central region, which we propose as an unresolved
inner echo. Multiple images were obtained in the F160W, F350LP, F555W, and F814W using the
Wide Field Camera 3. If the outer echo is produced by an interstellar dust sheet perpendicular
to the line of sight, it is located ∼800 pc in front of the SN. The dust for the inner echo is 0.45 pc
< d < 90 pc away from the SN. The inner echo color is consistent with typical interstellar dust
wavelength-dependent scattering cross-sections, while the outer echo color does not match the
predictions. Both dust sheets, if in the foreground, are optically thin for scattering, with the outer
echo sheet thickness consistent with the inferred extinction from peak brightness. Whether the
inner echo is from interstellar or circumstellar dust is ambiguous. Overall, the echo characteristics
are quite similar to previously observed SN Ia echoes.

Authors: D. Drozdov, M. D. Leising, P. A. Milne, J. Pearcy, A. G. Riess, L. M. Macri, G. L. Bryngelson, P. M. Garnavich

Read the paper on astro-ph

 

Wind mass transfer in S-type symbiotic binaries I. Focusing by the wind compression model Wednesday, October 29, 2014 - 10:21

Context: Luminosities of hot components in symbiotic binaries require accretion rates that are higher than those that can be achieved via a standard Bondi-Hoyle accretion. This implies that the wind mass transfer in symbiotic binaries has to be more efficient.

Aims: We suggest that the accretion rate onto the white dwarfs (WDs) in S-type symbiotic binaries can be enhanced sufficiently by focusing the wind from their slowly rotating normal giants towards the binary orbital plane.

Methods: We applied the wind compression model to the stellar wind of slowly rotating red giants in S-type symbiotic binaries.

Results: Our analysis reveals that for typical terminal velocities of the giant wind, 20 to 50 km/s, and measured rotational velocities between 6 and 10 km/s, the densities of the compressed wind at a typical distance of the accretor from its donor correspond to the mass-loss rate, which can be a factor of $\sim$10 higher than for the spherically symmetric wind. This allows the WD to accrete at rates of $10^{-8} - 10^{-7}$ M(Sun)/year, and thus to power its luminosity.

Conclusions: We show that the high wind-mass-transfer efficiency in S-type symbiotic stars can be caused by compression of the wind from their slowly rotating normal giants, whereas in D-type symbiotic stars, the high mass transfer ratio can be achieved via the gravitational focusing, which has recently been suggested for very slow winds in Mira-type binaries.

Authors: Augustin Skopal, Zuzana Carikova 

Read the paper on astro-ph

 

Existence of a group of “quiet” quasars confirmed Wednesday, October 29, 2014 - 09:42

Quasars appear to evolve with distance: the farther away one gets, the brighter they are. This could indicate that quasars extinguish over time or it could be the result of a simple observational bias masking a different reality: that gigantic quasars evolving very quickly, most of them already extinct, coexist with a quiet population that evolves at a much slower rhythm but which our technological limitations do not yet allow us to research.  

To solve this riddle it was necessary to look for low luminosity quasars at enormous  distances and to compare their characteristics with those of nearby quasars of equal luminosity, something thus far almost impossible to do, because it requires observing objects about a hundreds of times weaker than those we are used to studying at those distances.

The tremendous  light-gathering power of the GTC telescope, has recently enabled Sulentic and his team to obtain for the first time spectroscopic data from distant, low luminosity quasars similar to typical nearby ones. Data reliable enough to establish essential parameters such as chemical composition, mass of the central black hole or rate at which it absorbs matter.

Read the full story at IAA News

 

Georgia State Astronomers Image the Exploding Fireball Stage of a Nova Monday, October 27, 2014 - 07:06

MOUNT WILSON, Calif.–Astronomers at Georgia State University’s Center for High Angular Resolution Astronomy (CHARA) have observed the expanding thermonuclear fireball from a nova that erupted last year in the constellation Delphinus with unprecedented clarity.

The observations produced the first images of a nova during the early fireball stage and revealed how the structure of the ejected material evolves as the gas expands and cools. It appears the expansion is more complicated than simple models previously predicted, scientists said. The results of these observations, carried out by 37 researchers from 17 institutions and led by Georgia State astronomer Gail Schaefer, are published in the current issue of Nature.

Read the full press release

 

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