Chinese Astronomers Discover 591 High-velocity Stars with LAMOST and Gaia

591 high-velocity stars’ positions and orbits
Image by KONG Xiao of NAOC
Hi-res image

A research team, led by astronomers from National Astronomical Observatories of Chinese Academy of Sciences (NAOC), has discovered 591 high-velocity stars based on data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and Gaia, and 43 of them can even escape from the Galaxy.

The study was published online in The Astrophysical Journal Supplement Series on Dec. 17.

After the first high-velocity star was discovered in 2005, over 550 ones have been discovered with multiple telescopes in 15 years. "The 591 high-velocity stars discovered this time doubled the total number previously discovered, bringing the current total number exceeding 1,000," said Dr. LI Yinbi, lead author of the study. 

High-velocity stars are kind of fast-moving stars, and they can even escape from the Galaxy. "Though rare in the Milky Way, high-velocity stars, with unique kinematics, can provide deep insight into a wide range of Galactic science, from the central supermassive black hole to distant Galactic halo," said Prof. LU Youjun from NAOC, a co-author of this paper. 

LAMOST, the largest optical telescope in China, has the highest spectral acquisition rate in the world and can observe about 4,000 celestial targets in one single exposure. It began regular surveys in 2012, and established the largest spectra database in the world.

Gaia is a space-based mission in the science program of the European Space Agency (ESA) launched in 2013. It provided astrometric parameters for over 1.3 billion sources, which is the largest database of astrometric parameters. "The two massive databases provide us unprecedented opportunity to find more high-velocity stars, and we did it," said Prof. LUO Ali from NAOC, a co-author of this research. 

From the kinematics and chemistries, the research team found that the 591 high-velocity stars were inner halo stars. "Their low metallicities indicate that the bulk of the stellar halo formed as a consequence of the accretion and tidal disruption of dwarf galaxies," said Prof. ZHAO Gang from NAOC, a co-author of the study. 

The discovery of these high-velocity stars tells us that the combination of multiple large surveys in the future will help us to discover more high-velocity stars and other rare stars, which will be used to study the unsolved mystery about our Galaxy.

Contact

U AngU Ang
National Astronomical Observatories of China
E-mail: annxu@nao.cas.cn

Reference:

• 591 High-velocity Stars in the Galactic Halo Selected from LAMOST DR7 and Gaia DR2

Source: Chinese Academy of Sciences/Newsroom

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Primordial black holes and the search for dark matter from the multiverse

Fig1. Baby universes branching off of our universe shortly after the Big Bang appear to us as black holes.
Credit：Kavli IPMU

Fig2. Hyper Suprime-Cam (HSC) is a gigantic digital camera on the Subaru Telescope
Credit：HSC project / NAOJ

Fig3. The Subaru Telescope in Hawaii.
Credit：NAOJ

Fig4. A star in the Andromeda galaxy temporarily becomes brighter if a primordial black hole passes in front of the star, focusing its light in accordance with the theory of gravity. (Credit: Kavli IPMU/HSC Collaboration)

 

The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) is home to many interdisciplinary projects which benefit from the synergy of a wide range of expertise available at the institute. One such project is the study of black holes that could have formed in the early universe, before stars and galaxies were born.  

Such primordial black holes (PBHs) could account for all or part of dark matter, be responsible for some of the observed gravitational waves signals, and seed supermassive black holes found in the center of our Galaxy and other galaxies. They could also play a role in the synthesis of heavy elements when they collide with neutron stars and destroy them, releasing neutron-rich material. In particular, there is an exciting possibility that the mysterious dark matter, which accounts for most of the matter in the universe, is composed of primordial black holes. The 2020 Nobel Prize in physics was awarded to a theorist, Roger Penrose, and two astronomers, Reinhard Genzel and Andrea Ghez, for their discoveries that confirmed the existence of black holes. Since black holes are known to exist in nature, they make a very appealing candidate for dark matter. 

The recent progress in fundamental theory, astrophysics, and astronomical observations in search of PBHs has been made by an international team of particle physicists, cosmologists and astronomers, including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.

To learn more about primordial black holes, the research team looked at the early universe for clues. The early universe was so dense that any positive density fluctuation of more than 50 percent would create a black hole. However, cosmological perturbations that seeded galaxies are known to be much smaller. Nevertheless, a number of processes in the early universe could have created the right conditions for the black holes to form.  

One exciting possibility is that primordial black holes could form from the “baby universes” created during inflation, a period of rapid expansion that is believed to be responsible for seeding the structures we observe today, such as galaxies and clusters of galaxies. During inflation, baby universes can branch off of our universe. A small baby (or “daughter”) universe would eventually collapse, but the large amount of energy released in the small volume causes a black hole to form.  

An even more peculiar fate awaits a bigger baby universe. If it is bigger than some critical size, Einstein's theory of gravity allows the baby universe to exist in a state that appears different to an observer on the inside and the outside. An internal observer sees it as an expanding universe, while an outside observer (such as us) sees it as a black hole. In either case, the big and the small baby universes are seen by us as primordial black holes, which conceal the underlying structure of multiple universes behind their “event horizons.” The event horizon is a boundary below which everything, even light, is trapped and cannot escape the black hole. 

In their paper, the team described a novel scenario for PBH formation and showed that the black holes from the “multiverse” scenario can be found using the Hyper Suprime-Cam (HSC) of the 8.2m Subaru Telescope, a gigantic digital camera - - the management of which Kavli IPMU has played a crucial role - - near the 4,200 meter summit of Mt. Mauna Kea in Hawaii. Their work is an exciting extension of the HSC search of PBH that Masahiro Takada, a Principal Investigator at the Kavli IPMU, and his team are pursuing. The HSC team has recently reported leading constraints on the existence of PBHs in Niikura, Takada et. al. Nature Astronomy 3, 524–534 (2019)

Why was the HSC indispensable in this research? The HSC has a unique capability to image the entire Andromeda galaxy every few minutes. If a black hole passes through the line of sight to one of the stars, the black hole’s gravity bends the light rays and makes the star appear brighter than before for a short period of time. The duration of the star’s brightening tells the astronomers the mass of the black hole. With HSC observations, one can simultaneously observe one hundred million stars, casting a wide net for primordial black holes that may be crossing one of the lines of sight.  

The first HSC observations have already reported a very intriguing candidate event consistent with a PBH from the “multiverse,” with a black hole mass comparable to the mass of the Moon. Encouraged by this first sign, and guided by the new theoretical understanding, the team is conducting a new round of observations to extend the search and to provide a definitive test of whether PBHs from the multiverse scenario can account for all dark matter.  

Source: Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)

 

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Paper details

Journal: Physical Review Letters
Title: Exploring Primordial Black Holes from the Multiverse with Optical Telescopes
Authors: Alexander Kusenko (1, 2), Misao Sasaki (2, 3, 4), Sunao Sugiyama (2, 5), Masahiro Takada (2), Volodymyr Takhistov (1,2), and Edoardo Vitagliano (1)

Author affiliation: 

1. Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095-1547, USA 
2. Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
3. Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan 
4. Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 10617, Taiwan 
5. Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

DOI: https://doi.org/10.1103/PhysRevLett.125.181304  (October 30, 2020)
Abstract of the paper: (Physical Review Letters)
Preprint: (arXiv.org page)  

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Research contact:

Alexander Kusenko
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Visiting Senior Scientist
Department of Physics & Astronomy, University of California, Los Angeles
Professor
E-mail: kusenko@ucla.edu

Misao Sasaki
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Deputy Director
Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University
Leung Center for Cosmology and Particle Astrophysics, National Taiwan University
E-mail: misao.sasaki@ipmu.jp

Sunao Sugiyama
Graduate Student
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Department of Physics, The University of Tokyo
E-mail: sunao.sugiyama@ipmu.jp

Masahiro Takada
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Principal Investigator
E-mail: masahiro.takada@ipmu.jp

Volodymyr Takhistov
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
Project Researcher / Kavli IPMU Fellow
E-mail: volodymyr.takhistov@ipmu.jp

Media contact:

John Amari
Press officer 
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
E-mail: press@ipmu.jp
TEL: 080-4056-2767 

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Faint Remnant Threads

NGC 1947
Credit: ESA/Hubble & NASA, D. Rosario
Acknowledgement: L. Shatz

This unusual lenticular galaxy, known as NGC 1947, has lost almost all the gas and dust from its signature spiral arms, which used to orbit around its centre. Discovered almost 200 years ago by James Dunlop, a Scottish-born astronomer who later studied the sky from Australia, NGC 1947 can only be seen from the southern hemisphere, in the constellation Dorado (The Dolphinfish).

Residing around 40 million light-years away from Earth, this galaxy shows off its structure by backlighting its remaining faint gas and dust disc with millions of stars. In this picture, taken with the NASA/ESA Hubble Space Telescope, the faint remnants of the galaxy’s spiral arms can still be made out in the stretched thin threads of dark gas encircling it. Without most of its star-forming material, it is unlikely that many new stars will be born within NGC 1947, leaving this galaxy to continue fading with time.

Source: ESA/Hubble/powt

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SCExAO/CHARIS Nets its First Discovery

Figure 1: Direct image of HD 33632 Ab with SCExAO/CHARIS. The companion (marked as "b") lies at a separation of about 20 AU from its star (located at the white cross), similar to the separations from the Sun to Uranus and Neptune in our solar system (Credit: T. Currie, NAOJ/NASA-Ames)

The Subaru Telescope's state-of-the-art exoplanet imaging system – the SCExAO adaptive optics module coupled with the CHARIS integral field spectrograph – has seen two full years of Open Use operation. Now, this new system has gained its first discovery and demonstrated a new approach to best selecting stars with imageable planets and other low-mass companions like brown dwarfs (failed stars).

The newly-discovered object, a brown dwarf named HD 33632 Ab, orbits a 1.5 billion year-old near-twin of the Sun star about 86 light-years from the Earth (Figure 1). It joins one of the few known imaged substellar companions orbiting Sun-like stars on solar system-like (Mercury-to-Pluto) scales. 

SCExAO/CHARIS data taken in October 2018 and complemented a month later by Keck Observatory data, revealed a detection of this object at a separation of about 20 AU (astronomical unit, the distance between the Sun and the Earth) from its host star. Follow-up, more intensive SCExAO/CHARIS data taken on August 31 and September 1 of this year, during the COVID-19 pandemic, confirmed that HD 33632 Ab exists and is a gravitationally bound companion, not an unrelated background star. The CHARIS spectrum for HD 33632 Ab has a jagged, sawtooth-like shape, indicative of water and carbon monoxide molecules (Figure 2 left).

"Thanks to SCExAO/CHARIS's incredibly sharp images, we can not only see HD 33632 Ab but get ultra-precise measurements for its position and its spectrum, which gives important clues about its atmospheric properties and its dynamics," said Thayne Currie, an affiliated researcher at Subaru, and lead author of this study.

Figure 2: Properties of HD 33632 Ab from SCExAO/CHARIS data. (left) The spectrum of HD 33632 Ab, which is shaped by absorption from water and carbon monoxide molecules in the companion's atmosphere. (right) Modeling the orbit of HD 33632 Ab and providing a direct constraint on the companion's mass. The thick black oval shows the best-fit orbit for HD 33632 Ab with open circles representing predicted locations of the companion; other thin ovals represent other possible orbits. The orbits are color-coded by the predicted mass of HD 33632 Ab. (Credit: T. Currie, NAOJ/NASA-Ames; T. Brandt, UCSB)

Unlike nearly all other faint directly-imaged companions, HD 33632 Ab has a directly determined mass instead of a mass inferred from uncertain models predicting a planet/brown dwarf's mass based on its brightness at a given age. All planets or brown dwarfs orbiting their host stars cause the star to accelerate towards it due to the force of gravity. The ultra-sensitive Gaia astrometry satellite and its predecessor astrometry mission (Hipparcos) revealed that the star around which HD 33632 Ab orbits (HD 33632 A) shows an acceleration hinting at the presence of some companion, which SCExAO/CHARIS has now imaged.

"This is the first time we have found a brown dwarf by looking around a star that is being tugged across the sky. Finding a brown dwarf always involves luck, but this time we were able to stack the odds," adds Timothy Brandt, assistant professor of physics at the University of California-Santa Barbara, coauthor, and expert on Gaia/Hipparcos astrometry data.

Modeling the Gaia/Hipparcos absolute astrometry for the star and astrometry for HD 33632 Ab from Keck and Subaru telescope data together provided a precise dynamical mass for the companion of ~46 Jupiter masses (Figure2 right). This mass is significantly higher than the limit usually thought to separate planets from brown dwarfs (13-14 Jupiter masses), although the object also has a low, more planet-like eccentricity.

HD 33632 Ab could be key reference point for understanding the atmospheres of the first imaged and best studied extrasolar planets, which orbit a star called HR 8799 and were discovered from Maunakea in 2008 and 2010. The HD 33632 system is much older than the youthful HR 8799 (40 million years old). While HD 33632 Ab is more massive than the HR 8799 planets and has a higher surface gravity, it likely has a temperature very similar to these planets. Furthermore, we have a direct mass measurement for HD 33632 Ab and also good constraints on the mass for the HR 8799 planets through other analyses. Thus, HD 33632 Ab and the HR 8799 planets together may provide a critical insight into how substellar atmospheres (planets and brown dwarfs) at a given temperature differ at a range of ages and gravities. Their mass measurements then allow us to directly link these observational differences to bulk properties, i.e., masses.

"The atmospheres of planets like HR 8799's are notoriously hard to understand and likely have very peculiar properties like thick clouds, which have proven hard to model. Having a good reference point like our SCExAO-discovered companion is crucial to understanding this and other objects much better," said Currie.

Finally, this program shows the power of approach to identifying stars that likely host imageable planets and brown dwarfs. Most direct imaging searches are 'blind' searches, targeting some subset of stars within some age range or within a common star forming region. Imaging surveys conducted with predecessor instruments like the Gemini Planet Imager on Gemini South telescope in Chile and SPHERE on the Very Large Telescope also in Chile show that the detection rate of companions with these blind surveys is very low (a few percent). The research team is carrying out a different kind of search. Specifically, they are focusing on stars, drawn from a carefully selected sample made by coauthor Timothy Brandt, that show an acceleration seen in Gaia data. This acceleration is indirect evidence that there is a massive orbiting companion that is tugging on the star. HD 33632 Ab's detection represents a proof-in-concept of this approach. While this survey has just started with SCExAO, the team already has identified multiple new candidate companions, with a detection rate significantly higher than from a blind approach.

"These observations could greatly expand the discoveries by the previous successful SEEDS survey with AO188 and HiCIAO. The SCExAO and CHARIS combination will keep the Subaru telescope at the forefront of the direct imaging of exoplanets and brown dwarfs," said Masayuki Kuzuhara and Motohide Tamura from the Astrobiology Center at the National Institutes of Natural Sciences.

Figure 3: SCExAO and CHARIS at the Nasmyth focus at the Subaru Telescope on Maunakea. Credit: Princeton University CHARIS team/NAOJ

This research was published in the Astrophysical Journal Letters on November 30, 2020 (Currie et al. "SCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-Mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star".)

Relevant Links

• SCExAO/CHARIS Nets its First Discovery (Astrobiology Center December 11, 2020 press release)
• Direct Image of Newly-discovered Brown Dwarf Captured (W. M. Keck Observatory December 11, 2020 press release)

 

 Source: Subaru Telescope

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A Blazar In the Early Universe

VLBA image of the blazar PSO J0309+27, 12.8 billion light-years from Earth.
Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF. Hi-Res File

 

Full size image for download: VLBA image of the blazar PSO J0309+27
Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF.  Hi-Res File

The VLBA image of the blazar PSO J0309+27 is composed of data from three observations made at different radio frequencies. Red is from an observation at 1.5 GHz; green from 5 GHz; and blue from 8.4 GHz. The lower-frequency, or longer wavelength, data show the large-scale structure of the object; the intermediate- and higher-frequency data reveal increasingly smaller structures invisible to the VLBA at the lower frequency. Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF. Hi-Res File

The blazar PSO J0309+27 is in the constellation Aries.
Credit: Bill Saxton, NRAO/AUI/NSF.  Hi-Res File

The supersharp radio “vision” of the National Science Foundation’s Very Long Baseline Array (VLBA) has revealed previously unseen details in a jet of material ejected at three-quarters the speed of light from the core of a galaxy some 12.8 billion light-years from Earth. The galaxy, dubbed PSO J0309+27, is a blazar, with its jet pointed toward Earth, and is the brightest radio-emitting blazar yet seen at such a distance. It also is the second-brightest X-ray emitting blazar at such a distance.

In this image, the brightest radio emission comes from the galaxy’s core, at bottom right. The jet is propelled by the gravitational energy of a supermassive black hole at the core, and moves outward, toward the upper left. The jet seen here extends some 1,600 light-years, and shows structure within it.

At this distance, PSO J0309+27 is seen as it was when the universe was less than a billion years old, or just over 7 percent of its current age.

An international team of astronomers led by Cristiana Spingola of the University of Bologna in Italy, observed the galaxy in April and May of 2020. Their analysis of the object’s properties provides support for some theoretical models for why blazars are rare in the early universe. The researchers reported their results in the journal Astronomy & Astrophysics.

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

Scientific Paper

Media Contact:

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

 

Source:  National Radio Astronomy Observatory (NRAO)/News

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Astronomers Spot Farthest Galaxy Known in the Universe

An artist’s conception of the most distant galaxy with a gamma-ray burst
Credit: Jingchuan Yu

Maunakea, Hawaii – An international team of astronomers using W. M. Keck Observatory have spectroscopic confirmation of the most distant astrophysical object known to date.

The researchers, led by Professor Linhua Jiang at the Kavli Institute for Astronomy and Astrophysics at Peking University, obtained near-infrared spectra with the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) on the Keck I telescope and successfully measured the distance of a very faint galaxy located 13.4 billion light-years away (redshift of z = 10.957).

Named GN-z11, the galaxy was generally believed to be at a redshift greater than 10, probably closer to 11, based on existing data from NASA’s Hubble Space Telescope. But its exact redshift remained unclear, until now.

The results of the study, which are based on observations made under the time exchange program between Keck Observatory and Subaru Telescope on Maunakea, are published in the December 14, 2020 issue of the journal Nature Astronomy.

During their observations at Keck Observatory, the team also serendipitously detected a bright burst coming from the galaxy. After performing a comprehensive analysis, the team ruled out the possibility that the flash was from any known sources such as man-made satellites or moving objects in the solar system and determined it may have been produced by a gamma-ray burst.

A paper regarding this possible bright ultraviolet flash from GN-z11 is also published in the December 14, 2020 issue of Nature Astronomy.

Both studies are important to understanding the formation of stars and galaxies in the very early universe.

Source:  W.M. Keck Observatory/News

Learn more:

• “Spectroscopic Confirmation of the Most Distant Galaxy at Redshift 10.957” (Subaru Telescope Press Release, December 14, 2020)
• “Spectroscopic Confirmation of the Most Distant Galaxy at Redshift 10.957” (The Kavli Institute for Astronomy and Astrophysics at Peking University Press Release, December 15, 2020)
• “The Farthest Galaxy in the Universe” (The University of Tokyo Press Release, December 15, 2020)

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About MOSFIRE

The Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), gathers thousands of spectra from objects spanning a variety of distances, environments and physical conditions. What makes this large, vacuum-cryogenic instrument unique is its ability to select up to 46 individual objects in the field of view and then record the infrared spectrum of all 46 objects simultaneously. When a new field is selected, a robotic mechanism inside the vacuum chamber reconfigures the distribution of tiny slits in the focal plane in under six minutes. Eight years in the making with First Light in 2012, MOSFIRE’s early performance results range from the discovery of ultra-cool, nearby substellar mass objects, to the detection of oxygen in young galaxies only two billion years after the Big Bang. MOSFIRE was made possible by funding provided by the National Science Foundation. It is currently the most in-demand instrument at Keck Observatory.

About W. M. Keck Observatory

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

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Detailing the Formation of Distant Solar Systems with NASA's Webb Telescope

PDS 70 is approximately 370 light-years away and features a large gap in its inner ring. The European Southern Observatory's Very Large Telescope provided the first clear image of a planet forming around the central star in 2018. The planet is a bright point to the right of the center of the image. The central star is black since its light was blocked by an instrument known as a coronagraph. A second planet has also been detected. This system is a future target of NASA’s James Webb Space Telescope. Credit: ESO/A. Müller et al.

This infographic is an simplified artistic representation of planet formation, following the format of a baking recipe.

Credits: L. Hustak (STScI) .
Hi-res image

We live in a mature solar system—eight planets and several dwarf planets (like Pluto) have formed, the latter within the rock- and debris-filled region known as the Kuiper Belt. If we could turn back time, what would we see as our solar system formed? While we can’t answer this question directly, researchers can study other systems that are actively forming—along with the mix of gas and dust that encircles their still-forming stars—to learn about this process.

A team led by Dr. Thomas Henning of the Max Planck Institute for Astronomy in Heidelberg, Germany, will employ NASA's upcoming James Webb Space Telescope to survey more than 50 planet-forming disks in various stages of growth to determine which molecules are present and ideally pinpoint similarities, helping to shape what we know about how solar systems assemble.

Their research with Webb will specifically focus on the inner disks of relatively nearby, forming systems. Although information about these regions has been obtained by previous telescopes, none match Webb's sensitivity, which means many more details will pour in for the first time. Plus, Webb's space-based location about a million miles (1.5 million kilometers) from Earth will give it an unobstructed view of its targets. "Webb will provide unique data that we can't get any other way," said Inga Kamp of the Kapteyn Astronomical Institute of the University of Groningen in the Netherlands. "Its observations will provide molecular inventories of the inner disks of these solar systems."

This research program will primarily gather data in the form of spectra. Spectra are like rainbows—they spread out light into its component wavelengths to reveal high-resolution information about the temperatures, speeds, and compositions of the gas and dust. This incredibly rich information will allow the researchers to construct far more detailed models of what is present in the inner disks—and where. "If you apply a model to these spectra, you can find out where molecules are located and what their temperatures are," Henning explained.

These observations will be incredibly valuable in helping the researchers pinpoint similarities and differences among these planet-forming disks, which are also known as protoplanetary disks. "What can we learn from spectroscopy that we can't learn from imaging? Everything!" Ewine van Dishoeck of Leiden University in the Netherlands exclaimed. "One spectrum is worth a thousand images."

A 'Mountain' of New Data

Researchers have long studied protoplanetary disks in a variety of wavelengths of light, from radio to near-infrared. Some of the team's existing data are from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which collects radio light. ALMA excels at constructing images of the outer disks. If you were to compare the span of their outer disks to the size of our Solar System, this region is past Saturn's orbit. Webb's data will complete the picture by helping researchers model the inner disks.

Some data already exist about these inner disks—NASA's retired Spitzer Space Telescope served as a pathfinder—but Webb's sensitivity and resolution are required to identify the precise quantities of each molecule as well as the elemental compositions of the gas with its data, known as spectra. "What used to be a very blurry peak in the spectrum will consist of hundreds if not thousands of detailed spectral lines," van Dishoeck said.

Webb's specialty in mid-infrared light is particularly important. It will enable researchers to identify the "fingerprints" of molecules like water, carbon dioxide, methane, and ammonia—which can't be identified with any other existing instruments. The observatory will also determine how starlight impacts the chemistry and physical structures of the disks.

Protoplanetary disks are complex systems. As they form, their mix of gas and dust is distributed into rings across the system. Their materials travel from the outer disk to the inner disk—but how? "The inner portion of the disk is a very dynamic place," explains Tom Ray of the Dublin Institute for Advanced Studies in Ireland. "It's not only where terrestrial-type planets form, but it's also where supersonic jets are launched by the star."

Jets emitted by the star lead to a mixing of elements in the inner and outer disks, both by sending out particles and permitting other particles to move inward. "We think that as material leaves, it loses its spin, or angular momentum, and that this allows other material to move inward," Ray continued. "These exchanges of material will obviously impact the chemistry of the inner disk, which we’re excited to explore with Webb."

Exciting Insights Await

PDS 70 is farther at 370 light-years away. It also has a large gap in its inner ring, plus data have revealed that two forming planets, known as protoplanets, are present and gathering material. "Webb's mid-infrared measurements will help us refine what we know about them, as well as the material around them," Kamp explained.

With dozens of targets on their list, it's difficult for team members to play favorites. "I love them all," Henning said. "One question I'd like to answer concerns the connection between the composition of planet-forming disks and the planets themselves. With Webb, we will observe far more detail about which types of material are available for a potential planet to accrete."

After refining the data, his team will apply the discrete data points to models. "This will allow us to do a graphic reconstruction of these systems," he continued. These models will be shared with the astronomical community, enabling other scientists to examine the data, and make their own projections or glean new findings. These studies will be conducted through a Guaranteed Time Observations (GTO) program.

The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

By Claire Blome
Space Telescope Science Institute, Baltimore, Md.

Editor: Lynn Jenner

Source: NASA/Solar System and Beyond

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A pair of lonely planet-like objects born like stars

Artist’s composition of the two brown dwarfs, in the foreground Oph 98B in purple, in the background Oph 98A in red. Credit: Thibaut Roger

An international research team led by the University of Bern has discovered an exotic binary system composed of two young planet-like objects, orbiting around each other from a very large distance. Although these objects look like giant exoplanets, they formed in the same way as stars, proving that the mechanisms driving star formation can produce rogue worlds in unusual systems deprived of a Sun.

Star-forming processes sometimes create mysterious astronomical objects called brown dwarfs, which are smaller and colder than stars, and can have masses and temperatures down to those of exoplanets in the most extreme cases. Just like stars, brown dwarfs often wander alone through space, but can also be seen in binary systems, where two brown dwarfs orbit one another and travel together in the galaxy.

Researchers led by Clémence Fontanive from the Center for Space and Habitability (CSH) and the NCCR PlanetS discovered a curious starless binary system of brown dwarfs. The system CFHTWIR-Oph 98 (or Oph 98 for short) consists of the two very low-mass objects Oph 98 A and Oph 98 B. It is located 450 light-years away from Earth in the stellar association Ophiuchus. The researchers were surprised by the fact that Oph 98 A and B are orbiting each other from a strikingly large distance, about 5 times the distance between Pluto and the Sun, which corresponds to 200 times the distance between the Earth and the Sun. The study has just been published in The Astrophysical Journal Letters.

Extremely low masses and a very large separation

The pair is a rare example of two objects similar in many aspects to extra-solar giant planets, orbiting around each other with no parent star. The more massive component, Oph 98 A, is a young brown dwarf with a mass of 15 times that of Jupiter, which is almost exactly on the boundary separating brown dwarfs from planets. Its companion, Oph 98 B, is only 8 times heavier than Jupiter.

Components of binary systems are tied by an invisible link called gravitational binding energy, and this bond gets stronger when objects are more massive or closer to one another. With extremely low masses and a very large separation, Oph 98 has the weakest binding energy of any binary system known to date.

Dr. Clémence Fontanive, Center for Space and Habitability (CSH) and NCCR PlanetS, University of Bern, 

Credit: University of Bern

Discovery thanks to data from Hubble

Clémence Fontanive and her colleagues discovered the companion to Oph 98 A using images from the Hubble Space Telescope. Fontanive says: “Low-mass brown dwarfs are very cold and emit very little light, only through infrared thermal radiation. This heat glow is extremely faint and red, and brown dwarfs are hence only visible in infrared light.” Furthermore, the stellar association in which the binary is located, Ophiuchus, is embedded in a dense, dusty cloud which scatters visible light. “Infrared observations are the only way to see through this dust”, explains the lead researcher. “Detecting a system like Oph 98 also requires a camera with a very high resolution, as the angle separating Oph 98 A and B is a thousand times smaller than the size of the moon in the sky,” she adds. The Hubble Space Telescope is among the few telescopes capable of observing objects as faint as these brown dwarfs, and able to resolve such tight angles.

Because brown dwarfs are cold enough, water vapor forms in their atmospheres, creating prominent features in the infrared that are commonly used to identify brown dwarfs. However, these water signatures cannot be easily detected from the surface of the Earth. Located above the atmosphere in the vacuum of space, Hubble allows to probe the existence of water vapor in astronomical objects. Fontanive explains: “Both objects looked very red and showed clear signs of water molecules. This immediately confirmed that the faint source we saw next to Oph 98 A was very likely to also be a cold brown dwarf, rather than a random star that happened to be aligned with the brown dwarf in the sky.”

The team also found images in which the binary was visible, collected 14 years ago with the Canada-France-Hawaii Telescope (CFHT) in Hawaii. “We observed the system again this summer from another Hawaiian observatory, the United Kingdom Infra-Red Telescope. Using these data, we were able to confirm that Oph 98 A and B are moving together across the sky over time, relative to other stars located behind them, which is evidence that they are bound to each other in a binary pair”, explains Fontanive.

An atypical result of star formation

The Oph 98 binary system formed only 3 million years ago in the nearby Ophiuchus stellar nursery, making it a newborn on astronomical timescales. The age of the system is much shorter than the typical time needed to build planets. Brown dwarfs like Oph 98 A are formed by the same mechanisms as stars. Despite Oph 98 B being the right size for a planet, the host Oph 98 A is too small to have a sufficiently large reservoir of material to build a planet that big. “This tells us that Oph 98 B, like its host, must have formed through the same mechanisms that produce stars and shows that the processes that create binary stars operate on scale-down versions all the way down to these planetary masses”, comments Clémence Fontanive.

With the discovery of two planet-like worlds – already uncommon products of star formation – bound to each other in such an extreme configuration, “we are really witnessing an incredibly rare output of stellar formation processes”, as Fontanive describes.

 

Source: National Centre of Competence in Research PlanetS (NCCR)/News

Dark Storm on Neptune Reverses Direction, Possibly Shedding a Fragment

Hubble Uncovers a Pair of Dark Vortices on Neptune 

Credits:  NASA, ESA, M.H. Wong (University of California, Berkeley), and A. Simon (NASA Goddard Space Flight Center).  Release images - Release Video

Rotation of Neptune

Astronomers using NASA's Hubble Space Telescope watched a mysterious dark vortex on Neptune abruptly steer away from a likely death on the giant blue planet.

The storm, which is wider than the Atlantic Ocean, was born in the planet's northern hemisphere and discovered by Hubble in 2018. Observations a year later showed that it began drifting southward toward the equator, where such storms are expected to vanish from sight. To the surprise of observers, Hubble spotted the vortex change direction by August 2020, doubling back to the north. Though Hubble has tracked similar dark spots over the past 30 years, this unpredictable atmospheric behavior is something new to see.

Equally as puzzling, the storm was not alone. Hubble spotted another smaller dark spot in January this year that temporarily appeared near its larger cousin. It might possibly have been a piece of the giant vortex that broke off, drifted away, and then disappeared in subsequent observations.

"We are excited about these observations because this smaller dark fragment is potentially part of the dark spot’s disruption process," said Michael H. Wong of the University of California at Berkeley. "This is a process that's never been observed. We have seen some other dark spots fading away and they're gone, but we've never seen anything disrupt, even though it’s predicted in computer simulations."

The large storm, which is 4,600 miles across, is the fourth dark spot Hubble has observed on Neptune since 1993. Two other dark storms were discovered by the Voyager 2 spacecraft in 1989 as it flew by the distant planet, but they had disappeared before Hubble could observe them. Since then, only Hubble has had the sharpness and sensitivity in visible light to track these elusive features, which have sequentially appeared and then faded away over a duration of about two years each. Hubble uncovered this latest storm in September 2018.

Wicked Weather

Neptune's dark vortices are high-pressure systems that can form at mid-latitudes and may then migrate toward the equator. They start out remaining stable due to Coriolis forces, which cause northern hemisphere storms to rotate clockwise, due to the planet's rotation. (These storms are unlike hurricanes on Earth, which rotate counterclockwise because they are low-pressure systems.) However, as a storm drifts toward the equator, the Coriolis effect weakens and the storm disintegrates. In computer simulations by several different teams, these storms follow a more-or-less straight path to the equator, until there is no Coriolis effect to hold them together. Unlike the simulations, the latest giant storm didn't migrate into the equatorial "kill zone."

"It was really exciting to see this one act like it's supposed to act and then all of a sudden it just stops and swings back," Wong said. "That was surprising."

Dark Spot Jr.

The Hubble observations also revealed that the dark vortex’s puzzling path reversal occurred at the same time that a new spot, informally deemed "dark spot jr.," appeared. The newest spot was slightly smaller than its cousin, measuring about 3,900 miles across. It was near the side of the main dark spot that faces the equator—the location that some simulations show a disruption would occur.

However, the timing of the smaller spot's emergence was unusual. "When I first saw the small spot, I thought the bigger one was being disrupted," Wong said. "I didn't think another vortex was forming because the small one is farther towards the equator. So it's within this unstable region. But we can't prove the two are related. It remains a complete mystery.

"It was also in January that the dark vortex stopped its motion and started moving northward again," Wong added. "Maybe by shedding that fragment, that was enough to stop it from moving towards the equator."

The researchers are continuing to analyze more data to determine whether remnants of dark spot jr. persisted through the rest of 2020.

Dark Storms Still Puzzling

It's still a mystery how these storms form, but this latest giant dark vortex is the best studied so far. The storm's dark appearance may be due to an elevated dark cloud layer and it could be telling astronomers about the storm's vertical structure.

Another unusual feature of the dark spot is the absence of bright companion clouds around it, which were present in Hubble images taken when the vortex was discovered in 2018. Apparently, the clouds disappeared when the vortex halted its southward journey. The bright clouds form when the flow of air is perturbed and diverted upward over the vortex, causing gases to likely freeze into methane ice crystals. The lack of clouds could be revealing information on how spots evolve, say researchers.

Weather Eye on the Outer Planets

Hubble snapped many of the images of the dark spots as part of the Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project, led by Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland, that annually captures global maps of our solar system's outer planets when they are closest to Earth in their orbits.

OPAL's key goals are to study long-term seasonal changes, as well as capture comparatively transitory events, such as the appearance of dark spots on Neptune or potentially Uranus. These dark storms may be so fleeting that in the past some of them may have appeared and faded during multi-year gaps in Hubble's observations of Neptune. The OPAL program ensures that astronomers won't miss another one.

"We wouldn't know anything about these latest dark spots if it wasn't for Hubble," Simon said. "We can now follow the large storm for years and watch its complete life cycle. If we didn't have Hubble, then we might think the Great Dark Spot seen by Voyager in 1989 is still there on Neptune, just like Jupiter's Great Red Spot. And, we wouldn't have known about the four other spots Hubble discovered." Wong will present the team's findings Dec. 15 at the fall meeting of the American Geophysical Union.

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.

Contacts:

Media Contacts:

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

Science Contacts:
Michael H. Wong
University of California, Berkeley, California
HubbleSite

Amy Simon
NASA Goddard Space Flight Center, Greenbelt, Maryland
amy.simon@nasa.gov

 References:

• NASA's Hubble Portal
• M.H. Wong et al. (2020) Presentation Abstract at Fall AGU Meeting
• Hubble Sees Neptune's Mysterious Shrinking Storm 

Source: HubbleSite/News

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A Radio Flare from Colliding Stars?

When neutron stars collide, the shell of expanding ejecta can interact with the surrounding interstellar medium, producing long-lived radio flaring. [NASA's Goddard Space Flight Center/CI Lab].Hi-res image

When a pair of neutron stars collide, they emit a fireworks show. Could some of the low-energy light produced in these mergers be detectable years later? A team of scientists thinks so — and they’re pretty sure they’ve found an example.

A Rainbow of Signals

In addition to gravitational waves, a slew of electromagnetic radiation is produced in the merger of two neutron stars, spanning the spectrum from gamma rays to radio waves.

In 2017, the now-famous neutron star collision GW170817 gave us a first look at this expected emission: it revealed a short gamma-ray burst, infrared and optical light from ejecta in a kilonova, and relatively short-lived X-ray and radio afterglows caused by high-speed outflows.

But there’s one expected type of emission that was missing from GW170817, and it’s never before been spotted in any neutron star collision: radio flaring.

Illustration of radio emission from a neutron star merger. During the merger, some neutron star matter is flung outward. This ejecta interacts with the interstellar gas, producing a years-long radio flare. [Lee et al. 2020].Hi-res image

Radio Secrets revealed 

Models of neutron star mergers predict that when ejecta are flung out from the stellar collision, they’ll expand into space, eventually running into the surrounding medium of interstellar gas and dust. The subsequent interaction of the ejecta with the interstellar medium should produce radio flaring.

The emission from these radio flares is expected to be quite long-lived — lasting for years or even decades — which means we could hope to find these signals long after the time of the explosion that produced them. But radio flares are also likely to be relatively faint, so we could only expect to spot flares from nearby collisions (within ~650 million light-years). Additionally, only mergers that occur in environments with dense surrounding gas and dust will light up brightly enough for us to spot.

With these constraints, it’s perhaps not surprising that we haven’t found any radio flares marking past mergers yet. But a team of scientists led by Kyung-hwan Lee (University of Florida) recently waded through decades of radio data from the Very Large Array — and in a recent publication, they’re announcing that one transient may be the first identified radio flare from a stellar collision.

Observational data for FIRST J1419+3940 and best-fit radio light curves at three different frequencies. The data are better fit by the neutron-star-merger model (solid lines) than the long-gamma-ray-burst model (dashed lines). [Lee et al. 2020] . Hi-res image

A Decade-Old Collisions

FIRST J141918.9+394036 is a radio transient located in a dwarf galaxy 280 million light-years away. Lee and collaborators compile survey data on this source spanning 23 years and evaluate possible explanations for the radio emission.

While this source could potentially be explained as a long-gamma-ray-burst afterglow — light from an off-axis jet produced by a collapsing star — the radio data aren’t fit best by this picture. Instead, the authors show via models that this transient’s light curve is best described as the decay of a radio flare, just as predicted from a neutron star merger. This means that FIRST J141918.9+394036 likely marks a decades-old collision of two stars.

Within a few years, further observations of FIRST J141918.9+394036 will allow us to better distinguish between models and confirm its nature. And as we find more signals like this one, we can use these observations to further understand the origin and physics of neutron star mergers — potentially illuminating everything from the formation channel of binaries to the equation of state for neutron stars.

Citation

“FIRST J1419+3940 as the First Observed Radio Flare from a Neutron Star Merger,” K. H. Lee et al 2020 ApJL 902 L23. doi:10.3847/2041-8213/abbb8a

 

Source: American Astronomical Society - NOVA

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That young but already mature entirely self-made galaxy

Color image of the galaxy C1-23152 at redshift z=3.352, when the Universe was 1.8 billion years old. The image is the sum of 3 images at different wavelengths taken with the Hubble Space Telescope.  C1-23152 appears a regular spheroidal galaxy, its light profile matches exactly those of typical elliptical galaxies in the local Universe. Its stellar mass is about 200 billions of stars like sun and it is formed in less than 500 million years.

So young and already so mature: thanks to observations obtained at the Large Binocular Telescope, an international team of researchers coordinated by Paolo Saracco of the Istituto Nazionale di Astrofisica (INAF, Italy) was able to reconstruct the wild evolutionary history of an extremely massive galaxy that existed 12 billions years ago, when the Universe was only 1,8 billions years old, less than 13% of the present age. This galaxy, dubbed C1-23152, formed in "just" 500 million years, an incredibly short time to give rise to a mass of about 200 billion suns. To do so, it produced as many as 450 stars per year, more than one per day, a star formation rate almost 300 times higher than the current rate in our galaxy, the Milky Way.  The information obtained from this study will be fundamental for galaxy formation models for which the nature of objects such as C1-23152 is still difficult to account for.

The most massive galaxies that we observe in the Universe reach masses several hundred billion times that of the Sun and although they are numerically just one third of all galaxies, they contain more than 70% of the stars in the Universe. For this reason, how and how rapidly these galaxies formed are among the most debated questions of modern astrophysics. The current model of galaxy formation - the so-called hierarchical model - predicts that smaller galaxies formed earlier, while more massive systems formed later, through subsequent mergers of the pre-existing smaller galaxies. On the other hand, some of the properties of the most massive galaxies observed in the local Universe, such as the age of their stellar populations, suggest instead that they were formed at early epochs. Unfortunately, the variety of evolutionary phenomena that galaxies can undergo during their lives does not allow us to uniquely define, through studies conducted in the nearby Universe, the way in which they formed, leaving large margins of uncertainty. However, an answer to these questions can come from the study of the properties of massive galaxies in the early Universe, as close as possible to the time when they formed most of their mass.

Seventeen hours of spectroscopic observations with the Large Binocular Telescope (LBT) of the elliptical galaxy C1-23152, previously identified at a distance at which the Universe age was less than 13% of its current age, allowed Saracco’s team to reconstruct its evolutionary history. “The data show that the formation time of C1-23152, that is the time elapsed between the formation of the first stars from the pre-existing gas to the moment when the star formation has almost completely ceased, is less than 500 million of years” says Paolo Saracco, researcher at INAF in Milan and first author of the article published in The Astrophysical Journal. “Also, from the data collected with LBT we were able to establish that in this short time, corresponding to less than 4 hundredths of the age of the Universe, the galaxy formed a mass equal to about 200 billion stars like the Sun, that is about 450 suns per year. Our galaxy, the Milky Way, now forms no more than two a year", adds Danilo Marchesini, full professor at Tufts University and second author of the article. But that is not all. The large amount of information collected allowed the team to quantify for the first time in a galaxy so distant the abundance of chemical elements heavier than helium (the so-called metallicity): the stars of this galaxy have, surprisingly, a higher metallicity than that of the Sun, similar to that observed in the most massive galaxies in the Universe today.

Spectrum of galaxy C1-23152. The top panel shows the atmospheric transmission in the wavelength range of observations. In the middle panel the one-dimensional spectrum of galaxy C1-23152 is shown in the original form (dark-gray curve) and smoothed by a boxcar filter over three pixels (black curve) corresponding to the instrumental resolution. The main absorption and emission lines are marked by solid and dashed lines, respectively. The red curve is the best-fitting composite model obtained with STARLIGHT. The shaded gray regions are those masked in the fitting because of bad sky transmission or the presence of emission lines. For comparison, the bottom panel shows the observed spectrum of a typical post-starburst galaxy in the local Universe selected from the Sloan Digital Sky Survey (SDSS).

“These observations showed that the formation of the most massive galaxies in the Universe can occur extremely quickly, through an extremely intense star formation process in the early Universe, as for C1-23152", underlines Francesco La Barbera, researcher at INAF in Naples, in the team that conducted the study. "Understanding whether the scenario that describes the formation of C1-23152 is a particular case or whether, on the contrary, it is what happens for most of the most massive galaxies in the Universe is of fundamental importance since this would require a profound revision of the galaxy formation models”, adds Adriana Gargiulo, also a researcher at INAF in Milan and co-author of the study.

Likely formation scenario of massive elliptical galaxies like C1-23152. Massive primordial gas clouds, falling in the same region under the effect of gravitational force, collide triggering violent and massive star formation processes. The starburst phase is expected to last few hundreds of million years during which hundreds to thousands stars per year are formed, as for C1-23152. The resulting massive elliptical galaxy will then evolve with time, possibly experiencing different evolutionary phenomena. 

The formation of stellar masses as high as for C1-23152 requires both high masses of gas to convert into stars and particular physical conditions. A possible scenario hypothesized by the researchers is that massive primordial gas clouds, falling under the effect of gravitational force in the same region, collide, triggering violent and massive star formation processes. From the observational point of view, the precursors of the most massive galaxies could therefore be remote galaxies with a very high rate of star formation.

This image shows an example of starburst galaxies forming about a thousand of stars per year at the time of observation. This phase is most likely the formation phase of massive galaxies in the early Universe, like C1-23152.

"To test our hypotheses, the observations that the next generation of instrumentations will allow us to carry out will be decisive, in particular the James Webb Space Telescope (JWST) which will be launched in orbit at the end of 2021, and the Extremely Large Telescope (ELT) the largest ground-based telescope ever built, with a main mirror of 39 meters in diameter, which will be operational in 2026”, concludes Saracco.

Science Contacts:

• Paolo Saracco, paolo.saracco@inaf.it
• Danilo Marchesini, danilo.marchesini@tufts.edu
• Francesco La Barbera, francesco.labarbera@inaf.it
• Adriana Gargiulo, adriana.gargiulo@inaf.it

INAF Press Release:     https://www.media.inaf.it/2020/12/10/galassia-vega/

Publication link:  https://arxiv.org/pdf/2011.04657.pdf

 

 Source:  Large Binocular Telescope Observatory

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Nugget Galaxies Cross in the Sky

The canonical Einstein Cross, the quadruply lensed quasar Q2237+0305, is seen in this Hubble image. A new study has found two additional Einstein Crosses created by the lensing of compact galaxies. [NASA, ESA, and STScI]. Hi-res image

Diagram illustrating how light from a distant source can be bent by a foreground object to produce four identical images of the source. Click to enlarge. [NASA/ESA/D. Player (STScI)]

 

Detection and confirmation of the Einstein crosses, KIDS J232940-34092 (top two rows) and KIDS J122456+005048 (bottom two rows), via the KiDS survey and the MUSE integral field spectrograph on the VLT. Click to enlarge. [Napolitano et al. 2020]. Hi-res image

Seeing quadruple? In a rare phenomenon, some distant objects can appear as four copies arranged in an “Einstein cross”. A new study has found two more of these unusual sights — with an unexpected twist.

Searching for Rare Crosses

Gravitational lensing — the bending of light by the gravity of massive astronomical objects — can do some pretty strange things. One of lensing’s more striking creations is the Einstein cross, a configuration of four images of a distant, compact source created by the gravitational pull of a foreground object (which is usually visible in the center of the four images).

The canonical example of this phenomenon is the Einstein Cross, a gravitationally lensed object called QSO 2237+0305, seen in the cover image above. In this case, as with the majority of known Einstein crosses, the background source is a distant quasar — the small and incredibly bright nucleus of an active galaxy. But other sources can be lensed into Einstein crosses as well, under the right circumstances.

In a new study led by Nicola Napolitano (Sun Yat-sen University Zhuhai Campus, China), a team of scientists presents confirmation of two new Einstein crosses discovered within the 1,000 square degrees imaged in the Kilo-Degree Survey using the Very Large Telescope (VLT) in Chile. Einstein crosses are unusual enough to begin with, but these two discoveries are especially rare: the lensed sources are not quasars. Instead, they’re entire galaxies.

Galaxies, but Bite-Size

When a distant galaxy is lensed by a foreground object, it’s commonly smeared out into an an arc or a ring; this is because galaxies are large, extended objects. But if a galaxy is compact enough, the entire galaxy can be lensed into quadruple images instead of a smeared-out ring. Such is the case with Napolitano and collaborators’ new discoveries, KIDS J232940-340922 and KIDS J122456+005048: they’re both quadruply lensed compact galaxies known as post-blue nuggets.

What’s a blue nugget? This adorable categorization applies to a type of galaxy found only in the early universe. Blue nuggets are extremely small, quite massive, and undergoing a violent burst of star formation that produces lots of large, bright, blue stars.

Blue nuggets are thought to be suddenly quenched — their star formation is cut off — early in their evolution. As their star population then evolves, these post-blue nuggets then transition into red nuggets, compact collections of red stars that are theorized to become the cores of today’s large elliptical galaxies.

A Bright Future

By spectroscopically following up their Einstein cross discoveries, Napolitano and collaborators show that the two sources are both very compact, massive galaxies with low specific star formation rates. Their properties are consistent with post-blue nuggets currently undergoing quenching — which means that these Einstein crosses are excellent sources to study to learn about galaxy evolution.

The authors predict that, with future observatories like the Vera Rubin Observatory, Euclid, or the China Space Station Telescope, we may be able to find many thousands of Einstein crosses like these. There’s a lot to learn ahead!

Citation

“Discovery of Two Einstein Crosses from Massive Post-blue Nugget Galaxies at z > 1 in KiDS,” N. R. Napolitano et al 2020 ApJL 904 L31. doi:10.3847/2041-8213/abc95ba

 

Source: American Astronomical Society - NOVA 

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