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Short Gamma-Ray Burst Localized to Extremely Distant Galaxy (Astronomy)

Astronomers has observed an optical afterglow of a short gamma-ray burst, thought to be from the merger of two neutron stars, and localized it to a particular host galaxy, which is located 10 billion light-years away in the constellation of Coma Berenices. Dubbed GRB 181123B, the event occurred 3.8 billion years after the Big Bang. It is the second most-distant short gamma-ray burst ever detected and the most distant event with an optical afterglow.

Fig: The afterglow of GRB 181123B (marked with a circle), captured by the Gemini-North telescope. Image credit: Gemini Observatory / NOIRLab / NSF / AURA / K. Paterson & W. Fong, Northwestern University / Travis Rector, University of Alaska Anchorage / Mahdi Zamani / Davide de Martin.

Short gamma-ray bursts (SGRBs) are short-lived, highly-energetic bursts of gamma-ray light.

Tought to result from the merger of two neutron stars, they are cataclysmic events that are almost unfathomable in terms of their basic properties, emitting huge amounts of energy.

The gamma-ray light lasts for less than two seconds, while the optical light can last for a matter of hours before fading.

Therefore, rapid follow-up of the optical afterglow of these intense flashes of gamma-ray radiation is critical.

Astronomers typically only detect 7-8 SGRBs each year that are well-localized enough for further observations.

GRB 181123B was detected on November 23, 2018 by NASA’s Neil Gehrels Swift Observatory.

Within just a few hours after the detection and a worldwide alert, Northwestern University astronomer Kerry Paterson and colleagues quickly pointed the 8.1-m Gemini-North telescope, the 10-m Keck I telescope and the Multi-Mirror Telescope toward the location of GRB 181123B and were able to measure its very faint afterglow.

They were able to obtain deep observations of the burst mere hours after its discovery. The Gemini images were very sharp, allowing them to pinpoint the location to a specific galaxy in the Universe. They certainly did not expect to discover a distant SGRB, as they are extremely rare and very faint.

They perform ‘forensics’ with telescopes to understand its local environment, because what its home galaxy looks like can tell them a lot about the underlying physics of these systems.

Fig: An artist’s impression of how GRB 11823B compares to other short gamma-ray bursts. Except when they are detected by gravitational wave observatories, the gamma ray bursts can only be detected from Earth when their jets of energy are pointed towards us. Image credit: Gemini Observatory / NOIRLab / NSF / AURA / J. Pollard / K. Paterson & W. Fong, Northwestern University / Travis Rector, University of Alaska Anchorage / Mahdi Zamani / Davide de Martin.

After identifying the host galaxy of GRB 181123B and calculating the distance, the astronomers were able to determine key properties of the parent stellar populations within the galaxy that produced the event.

Because GRB 181123B appeared when the Universe was only about 30% of its current age — during an epoch known as ‘Cosmic High Noon’ — it offered a rare opportunity to study the neutron star mergers from when the Universe was a ‘teenager.’

When GRB 181123B occurred, the Universe was incredibly busy, with rapidly forming stars and fast-growing galaxies.

Massive binary stars need time to be born, evolve and die — finally turning into a pair of neutron stars that eventually merge.

References: K. Paterson, W. Fong, A. Nugent, A. Rouco Escorial, J. Leja, T. Laskar, R. Chornock, A. A. Miller, J. Scharwächter, S. B. Cenko, D. Perley, N. R. Tanvir, A. Levan, A. Cucchiara, B. E. Cobb, K. De, E. Berger, G. Terreran, K. D. Alexander, M. Nicholl, P. K. Blanchard, D. Cornish, “Discovery of the optical afterglow and host galaxy of short GRB181123B at z=1.754: Implications for Delay Time Distributions”, astrophysical journal, pp. 1-18, 2020..

Moon May Be 85 Million Years Younger than Previously Thought (Astronomy)

According to a new modeling study by M. Maurice & colleagues, Earth’s only natural satellite formed 4.425 billion years ago — around 85 million years later than previous estimates..

Fig: When the Moon formed into a sphere approximately 1,700 km in radius 4.425 billion years ago, its interior heated up considerably due to the energy released when it accreted. The rock melted and an ocean of magma, possibly more than 1,000 km deep, formed. Later, light rocks crystallized, which rose to the surface and formed a first crust on the Moon. This crust insulated the Moon from space, and the magma ocean beneath it cooled down slowly. Around 200 million years would pass before the Moon completely solidified. Image credit: NASA’s Goddard Space Flight Center.

According to the giant impact hypothesis, the Moon was created out of the debris left over from a catastrophic collision between the proto-Earth and a Mars-sized protoplanet called Theia.

This collision produced a lunar magma ocean and initiated the last event of core segregation on Earth. However, the timing of these events remains uncertain.

The scientists determined when the Moon was formed using a new, indirect method & they demonstrated that the lunar magma ocean quickly began to solidify and formed a crust of floating, lightweight crystals at the surface — its ‘interface’ with the cold space.

But under this insulating crust, which slowed down the further cooling and solidification of the magma ocean, the Moon remained molten for a long time.

Until now, scientists were unable to determine how long it took for the magma ocean to crystallize completely, which is why they could not conclude when the Moon originally formed.

To calculate the lifetime of the Moon’s magma ocean, the authors used a new computer model, which for the first time comprehensively considered the processes involved in the solidification of the magma.

& their results from the model showed that the Moon’s magma ocean was long-lived and took almost 200 million years to completely solidify into mantle rock. The time scale is much longer than calculated in previous studies. Older models gave a solidification period of only 35 million years.

To determine the age of the Moon, the team calculated how the composition of the magnesium- and iron-rich silicate minerals that formed during the solidification of the magma ocean changed over time.

The researchers discovered a drastic change in the composition of the remaining magma ocean as solidification progressed.

This finding is significant because it allowed them to link the formation of different types of rock on the Moon to a certain stage in the evolution of its magma ocean.

By comparing the measured composition of the Moon’s rocks with the predicted composition of the magma ocean from their model, they were able to trace the evolution of the ocean back to its starting point, the time at which the Moon was formed.

The results showed that the Moon was formed 4.425 billion years ago.

This age is in remarkable agreement with an age previously determined for the formation of Earth’s metallic core with the uranium-lead method, the point at which the formation of the Earth was completed.

References: M. Maurice, N. Tosi, S. Schwinger, D. Breuer and T. Kleine, “A long-lived magma ocean on a young Moon”, Science Advances 10 Jul 2020:
Vol. 6, no. 28..

Thermonuclear Supernova Ejects White Dwarf from Binary System (Astronomy)

A white dwarf star called SDSS J124043.01+671034.68 (SDSS J1240+6710) is traveling at 900,000 km/h (559,234 mph) through our Milky Way Galaxy. It also has a particularly low mass for a white dwarf — only 40% the mass of our Sun — which would be consistent with the loss of mass from a partial supernova. According to new research carried out by Boris T. Gänsicke and colleagues, SDSS J1240+6710 was most likely a member of a binary system that survived a so-called thermonuclear supernova event, which sent it and its companion flying through the Milky Way in opposite directions.

An artist’s impression of a thermonuclear supernova: the material ejected by the supernova will initially expand very rapidly, but then gradually slow down, forming an intricate giant bubble of hot glowing gas; eventually, the charred remains of the white dwarf that exploded will overtake these gaseous layers, and speed out onto its journey across our Milky Way Galaxy. Image credit: Mark Garlick / University of Warwick.

White dwarfs are the remaining cores of red giants after these huge stars have died and shed their outer layers, cooling over the course of billions of years.

The majority of white dwarfs have atmospheres composed almost entirely of hydrogen or helium, with occasional evidence of carbon or oxygen dredged up from the star’s core.

SDSS J1240+6710, which was discovered in 2015, lies 1,432 light-years away from us in the constellation of Draco.

Also known as WD 1238+674 and LSPM J1240+6710, the star was previously found to have an oxygen-dominated atmosphere with significant traces of neon, magnesium, and silicon. It is unique because it has all the key features of a white dwarf but it has this very high velocity and unusual abundances that make no sense when combined with its low mass.

Using the Cosmic Origin Spectrograph onboard the NASA/ESA Hubble Space Telescope, Professor Gaensicke and colleagues identified carbon, sodium, and aluminum in the atmosphere of SDSS J1240+6710, all of which are produced in the first thermonuclear reactions of a supernova.

However, there is a clear absence of what is known as the ‘iron group’ of elements, iron, nickel, chromium and manganese.

These heavier elements are normally cooked up from the lighter ones, and make up the defining features of thermonuclear supernovae.

The lack of iron group elements in SDSSJ1240+6710 suggests that the star only went through a partial supernova before the nuclear burning died out.

The authors theorize that the supernova disrupted the white dwarf’s orbit with its partner star when it very abruptly ejected a large proportion of its mass.

Both stars would have been carried off in opposite directions at their orbital velocities in a kind of slingshot maneuver. That would account for the star’s high velocity.

The best studied thermonuclear supernovae are the Type Ia. But there is growing evidence that thermonuclear supernovae can happen under very different conditions.

SDSSJ1240+6710 may be the survivor of a type of supernova that hasn’t yet been caught in the act.

Without the radioactive nickel that powers the long-lasting afterglow of the Type Ia supernovae, the explosion that sent SDSS1240+6710 hurtling across our Galaxy would have been a brief flash of light that would have been difficult to discover.

The study of thermonuclear supernovae is a huge field and there’s a vast amount of observational effort into finding supernovae in other galaxies. The difficulty is that we can see the star when it explodes but it’s very difficult to know its properties before it exploded.

The fact that such a low mass white dwarf went through carbon burning is a testimony of the effects of interacting binary evolution and its effect on the chemical evolution of the Universe.

References: Boris T Gänsicke, Detlev Koester, Roberto Raddi, Odette Toloza, S O Kepler, “SDSS J124043.01 + 671034.68: the partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?”, Monthly Notices of the Royal Astronomical Society, Volume 496, Issue 4, August 2020, Pages 4079–4086..

Astronomers Detect Spiral-Arm Structures around High-Mass Protostar (Astronomy)

New observations done by X.Chen and colleagues, of a high-mass protostar in the massive star-forming region G358.93-0.03 shed light on how these young stellar objects accumulate their mass.

Figure: An artist’s impression of the immediate vicinity of the massive protostar G358.93-0.03-MM1. Image credit: Xi Chen, Guangzhou University / Zhi-Yuan Ren, National Astronomical Observatories, Chinese Academy of Science.

High-mass protostars are thought to accumulate much of their mass via short, infrequent bursts of accretion. Such accretion events are rare and difficult to observe directly.

In a previous study, University of Tasmania’s Professor Simon Ellingsen and colleagues focused on a high-mass young stellar object called G358.93-0.03-MM1.

This protostar is embedded within G358.93-0.03, a massive star-forming region located approximately 22,000 light-years away in the constellation of Ophiuchus.

The astronomers managed to identify and observe an accretion burst in real time from its onset, a rare opportunity that helped prove the episodic accretion theory of stellar formation.

In the new study, they created a high resolution map of the molecular gas swirling around G358.93-0.03-MM1.

From their observations, they’re able to map gas close to the protostar in 3D, and it looks like the material flowing onto the star has formed a spiral structure, which provides an explanation as to why the accretion happens in bursts, rather than more steadily.

These protostars are in many ways the most important for the evolution of galaxies over cosmic time, but at the moment, they don’t have a good understanding of how they form.. Observing the formation of these giants is hard — there aren’t very many of them, they form quickly, and the formation is hidden deep within very dense gas clouds which blocks light at most wavelengths..

Their new observations are providing some of the most direct information as to how these stars accumulate their mass and are opening up an exciting new window to study these rare events..

G358.93-0.03-MM1 is the first example of a massive protostar whose sudden increase in brightness clearly coincides with the formation of a spiral, a structure that suggests an unstable, massive disk..

In conjunction with theoretical models, it is thus possible for the first time to establish a direct correlation between the variation in luminosity and the accretion of individual packets of matter from an unstable, massive disk.

This result suggests that disk-mediated accretion could therefore be regarded as a common mechanism for star formation of low-mass to high-mass stars.

References: Xi Chen, Andrej M. Sobolev, Zhi-Yuan Ren, Sergey Parfenov, Shari L. Breen, Simon P. Ellingsen, Zhi-Qiang Shen, Bin Li, Gordon C. MacLeod, Willem Baan, Crystal Brogan, Tomoya Hirota, Todd R. Hunter, Hendrik Linz, Karl Menten, Koichiro Sugiyama, Bringfried Stecklum, Yan Gong & Xingwu Zheng, “New maser species tracing spiral-arm accretion flows in a high-mass young stellar object”, Nature Astronomy (2020)

Astronomers Develop Method to Detect Tiny Black Holes in Outskirts of Our Solar System (Astronomy)

Amir Siraj, with Avi Loeb, have developed a new method to search for primordial black holes in the outer Solar System, based on accretion flares that result from impacts of small bodies from the Oort Cloud.

Fig: Siraj & Loeb explore the possibility that accretion flares resulting from the tidal disruption of small Oort Cloud bodies by a putative primordial black hole could power an observable optical signal that could be searched for with the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time. Image credit: ESO/Zdenek Bardon.

Anomalous orbits and clustering of detached trans-Neptunian objects in the outer Solar System suggest the possible existence of Planet Nine, a planet with a mass of 5 to 10 times that of Earth, at a distance of 400-800 AU from the Sun.

In 2019, astronomers Jakub Scholtz and James Unwin suggested that this hypothetical planet could potentially be a grapefruit-sized primordial black hole since the likelihood of trapping for a black hole may be comparable to that for a free-floating planet.

Planet Nine is a compelling explanation for the observed clustering of some objects beyond the orbit of Neptune..

If the existence of Planet Nine is confirmed through a direct electromagnetic search, it will be the first detection of a new planet in the Solar System in two centuries, not counting Pluto..

A failure to detect light from Planet Nine — or other recent models, such as the suggestion to send probes to measure gravitational influence — would make the black hole model intriguing..

The outskirts of the Solar System are our backyard. Finding Planet Nine is like discovering a cousin living in the shed behind your home which you never knew about..

It immediately raises questions: why is it there? How did it obtain its properties? Did it shape the Solar System history? Are there more like it?

In their new paper, Siraj and Professor Loeb found that if Planet Nine is a primordial black hole, its existence can be discovered by the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) due to brief accretion flares powered by small Oort Cloud bodies, which would be detected at a rate of at least a few per year.

In the vicinity of a black hole, small bodies that approach it will melt as a result of heating from the background accretion of gas from the interstellar medium onto the black hole.

Once they melt, the small bodies are subject to tidal disruption by the black hole, followed by accretion from the tidally disrupted body onto the black hole.

Because black holes are intrinsically dark, the radiation that matter emits on its way to the mouth of the black hole is our only way to illuminate this dark environment.

LSST is expected to have the sensitivity required to detect accretion flares, while current technology isn’t able to do so without guidance.

References: Amir Siraj, Abraham Loeb, “Searching for Black Holes in the Outer Solar System with LSST”, pp. 1-4, 2020..

New Class of Radio-Astronomical Objects Discovered: Odd Radio Circles (Astronomy)

An international team of astronomers has discovered an unexpected new class of radio-astronomical objects, consisting of a circular disk, which in some cases is limb-brightened, and sometimes contains a galaxy at its center. Named ‘Odd Radio Circles,’ these objects do not seem to correspond to any known type of astronomical object.

Fig: ASKAP radio continuum image of ORC 1 (contours) overlaid onto a DES 3-color composite image. Two galaxies of interest: ‘C’ lies near the center of ORC 1 and ‘S’ coincides with the southern radio peak. Image credit: Norris et al, arXiv: 2006.14805.

Circular features are well-known in radio-astronomical images, and usually represent a spherical object such as a supernova remnant, a planetary nebula, a shell around a star, or a face-on disk such as a protoplanetary disk or a star-forming galaxy.

They may also arise from imaging artifacts around bright astronomical objects.

Western Sydney University and CSIRO astronomer Ray Norris and his colleagues report the discovery of a class of circular feature in radio images that do not seem to correspond to any of these known types of object or artifact, but rather appear to be a new class of astronomical object.

The researchers spotted three ORCs — named ORCs 1, 2 and 3 — in images from the Pilot Survey of the Evolutionary Map of the Universe, which is an all-sky continuum survey using the Australian Square Kilometre Array Pathfinder telescope (ASKAP).

A further radio source, called ORC 4, was discovered in archival observations of the galaxy cluster Abell 2142 taken with the Giant MetreWave Radio Telescope (GMRT).

All four ORCs are similar in displaying a strong circular symmetry and none of them have obvious counterparts in optical, infrared and X-ray wavelengths.

They differ in that two of them have a central galaxy while two do not, and three of them (ORCs 1, 2 and 4) consist of a partly filled ring while one (ORC 3) seems to be a uniform disk. There is also the puzzling fact that two of them are very close together, implying that these two ORCs have a common cause.

If the central galaxy in ORC 4 is associated with the ring, then the ring is 4.2 billion light-years away and has a size of 1.1 by 0.9 million light-years.

Fig: ASKAP radio continuum images of ORCs 2 and 3 from the Pilot Survey of the Evolutionary Map of the Universe and of ORC 4 from GMRT archival data. On the left are gray-scale images, with the synthesized beam shown in the bottom left corner, and radio contours overlaid onto DES optical images on the right. Image credit: Norris et al.

They speculated that they may represent a spherical shock wave from an extra-galactic transient event. Several such classes of transient events, capable of producing a spherical shock wave, have recently been discovered, such as fast radio bursts, gamma-ray bursts, and neutron star mergers. However, because of the large angular size of the ORCs, any such transients would have taken place in the distant past.

It is also possible that the ORCs represent a new category of a known phenomenon, such as the jets of a radio galaxy or blazar when seen end-on, down the ‘barrel’ of the jet.

Alternatively, they may represent some remnant of a previous outflow from a radio galaxy.

However, no existing observations of this phenomenon closely resemble the ORCs in features such as the edge-brightening or the absence of a visual blazar or radio galaxy at the center.

References: Ray P. Norris, Huib T. Intema, Anna D. Kapinska, Baerbel S. Koribalski, Emil Lenc, L. Rudnick, Rami Alsaberi, Craig Anderson, G. E. Anderson, E. Crawford, Roland Crocker, Stefan W. Duchesne, Miroslav D. Filipovic, Andrew M. Hopkins, Natasha Hurley-Walker, Susumu Inoue, Kieran Luken, Peter Macgregor, Pero Manojlovic, Josh Marvil, Andrew N. OBrien, Wasim Raja, Devika Shobhana, Jordan D. Collier, Catherine Hale, Aidan Hotan, David McConnell, Vanessa Moss, Matthew Whiting, “Unexpected Circular Radio Objects at High Galactic Latitude”, pp. 1-32, 2020..

Hubble Spots Rare ‘Free-Floating Evaporating Gaseous Globule’ (Astronomy)

Astronomers using the NASA/ESA Hubble Space Telescope have captured an outstanding image of J025027.7+600849 (J0250 for short), a rare type of stellar nursery embedded within a nearby massive star-forming region.

Fig: This Hubble image shows the free-floating evaporating gaseous globule J025027.7+600849. The color image is made up of observations from Hubble’s Advanced Camera for Surveys (ACS) in the near-infrared and optical parts of the spectrum. Three filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / R. Sahai.

J0250 is located approximately 6,000 light-years away in the constellation of Cassiopeia.

This object resides in the open star cluster IC 1848, which, in turn, is embedded within the emission nebula Westerhout 5.

J0250 belongs to the recently-discovered class of star-forming nursery called free-floating evaporating gaseous globules (frEGGs).

When a massive new star — or stars — starts to shine while still within the cool molecular cloud from which it formed, its energetic radiation can ionize the cloud’s hydrogen and create a large, hot bubble of ionized gas.

Amazingly, located within this bubble of hot gas around a nearby massive star are the frEGGs — dark compact globules of dust and gas, some of which are also giving birth to low-mass stars.

The boundary between the cool, dusty frEGG and hot gas bubble is seen as the glowing purple/blue edges in this new Hubble image.

Learning more about these odd objects can help astronomers understand how stars like our Sun form under external influences..

In fact, our Sun may have even been born in a frEGG..

Earth’s Magnetic Field Can Switch Direction 10 Times Faster than Previously Thought (Physics)

According to recent study of Davies and colleagues, changes in the direction of Earth’s internally generated magnetic field may take place 10 times faster than previously thought..

Figure: Earth’s magnetic field lines. Image credit: NASA’s Goddard Space Flight Center.

The magnetic field of Earth is generated and maintained by a convective flow of molten metal that forms our planet’s outer core.

Motion of the liquid iron creates the electric currents that power the field, which not only helps guide navigational systems but also helps shield us from harmful extra terrestrial radiation and hold our atmosphere in place.

The geomagnetic field is constantly changing. To capture the evolution of the field back through geological time, geoscientists analyze the magnetic fields recorded by sediments, lava flows and human-made artifacts.

Accurately tracking the signal from Earth’s core field is extremely challenging and so the rates of field change estimated by these types of analysis are still debated.

Dr. Davies and his colleague, Professor Catherine Constable from the Scripps Institution of Oceanography, combined computer simulations of the geomagnetic field generation process with a reconstruction of time variations in the field spanning the last 100,000 years

Their results show that changes in the direction of the geomagnetic field reached rates that are up to 10 times larger than the fastest currently reported variations of up to one degree per year.

They demonstrate that these rapid changes are associated with local weakening of the magnetic field.

This means these changes have generally occurred around times when the field has reversed polarity or during geomagnetic excursions when the dipole axis — corresponding to field lines that emerge from one magnetic pole and converge at the other — moves far from the locations of the North and South geographic poles.

The clearest example of this is a sharp change in the geomagnetic field direction of roughly 2.5 degrees per year 39,000 years ago.

This shift was associated with locally weak field strength, in a confined spatial region just off the west coast of Central America, and followed the global Laschamp excursion, a short reversal of the Earth’s magnetic field roughly 41,000 years ago.

Similar events are identified in computer simulations of the field which can reveal many more details of their physical origin than the limited paleomagnetic reconstruction.

Their detailed analysis indicates that the fastest directional changes are associated with movement of reversed flux patches across the surface of the liquid core.

These patches are more prevalent at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas.

References: C.J. Davies & C.G. Constable. 2020. Rapid geomagnetic changes inferred from Earth observations and numerical simulations. Nat Commun 11, 3371; doi: 10.1038/s41467-020-16888-0..

Hubble Snaps Image of Barred Spiral Galaxy NGC 7513 (Astronomy)

The NASA/ESA Hubble Space Telescope has captured a striking photo of a bright, barred spiral galaxy called NGC 7513.

This Hubble image shows the barred spiral galaxy NGC 7513. The color image was made from separate exposures taken in the visible and infrared regions of the spectrum with Hubble’s Wide Field Camera 3 (WFC3). Three filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / M. Stiavelli.

NGC 7513 is located approximately 56 million light-years away in the southern constellation of Sculptor.

Discovered on September 24, 1864 by the German astronomer Albert Marth, the galaxy has a diameter of around 65,000 light-years.

While some galaxies, like the Milky Way and the Andromeda Galaxy, are caught in each other’s gravitational pull and will eventually merge together, the vast majority of galaxies in our Universe appear to be moving away from each other..

This phenomenon is due to the expansion of the Universe, and it is the space between galaxies that is stretching, rather than the galaxies themselves moving..

NGC 7513 is moving at the astounding speed of 1,564 km per second (3.5 million mph), and it is heading away from us..

For context, the Earth orbits the Sun at about 30 km per second (over 67,000 mph)..

Though NGC 7513’s apparent movement away from the Milky Way might seem strange, it is not that unusual..