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Experimental Vaccine Induces Anti-SARS-CoV-2 Immune Responses in All Participants (Medicine)

Dr. Lisa Jackson of Kaiser Permanente Washington Health Research Institute in Seattle and colleagues conducted a first-in-human Phase 1 clinical trial in healthy adults to evaluate the safety and immunogenicity of an investigational anti-SARS-CoV-2 vaccine called mRNA-1273. According to their report published in the New England Journal of Medicine, the vaccine candidate was generally well tolerated and prompted neutralizing antibody activity in all participants. The trial is supported by the NIH/National Institute of Allergy and Infectious Diseases (NIAID).

Fig: Colorized scanning electron micrograph of a cell (green) infected with SARS-CoV-2 virus particles (purple), isolated from a patient sample. Image credit: NIAID.

The mRNA-1273 vaccine candidate, manufactured by Moderna, Inc. of Cambridge, Massachusetts, is designed to induce neutralizing antibodies directed at a portion of SARS-CoV-2’s spike protein, which the virus uses to bind to and enter human cells.

In the preliminary report, Dr. Jackson and co-authors detailed the findings from the first 45 participants (18 to 55 years old) enrolled at the study sites in Seattle and at Emory University in Atlanta.

Three groups of 15 participants received two intramuscular injections in March and April 2020 of either 25, 100 or 250 micrograms (mcg) of the mRNA-1273 vaccine.

All the participants received one injection; 42 received both scheduled injections.

Regarding safety, no serious adverse events were reported.

More than half of the participants reported fatigue, headache, chills, myalgia or pain at the injection site.

Systemic adverse events were more common following the second vaccination and in those who received the highest vaccine dose.

Data on side effects and immune responses at various vaccine dosages informed the doses used or planned for use in the Phase 2 and 3 clinical trials of the investigational vaccine.

The interim analysis includes results of tests measuring levels of vaccine-induced neutralizing activity through day 43 after the second injection.

References: Lisa A. Jackson et al., “An mRNA Vaccine against SARS-CoV-2 – Preliminary Report”, New England Journal of Medicine, published online July 14, 2020..

CERN Physicists Discover Four-Charm-Quark Particle (Physics)

Physicists from CERN’s LHCb Collaboration have discovered a new tetraquark particle, named X(6900), composed of two charm quarks and two charm antiquarks.

Fig: X(6900), a tetraquark particle composed of two charm quarks and two charm antiquarks. Image credit: CERN.

Quarks are point-like elementary particles that typically come in packages of two (mesons) or three (baryons), the most familiar of which are the proton and neutron — each is made of three quarks.

There are six types — or flavors — of quark to choose from: up, down, strange, charm, bottom and top. Each of these also has an antimatter counterpart.

In their fundamental 1964 papers, American physicists Murray Gell-Mann and George Zweig proposed the quark model and mentioned the possibility of adding a quark-antiquark pair to a minimal meson or baryon quark configuration to form tetra- and pentaquarks.

It took 50 years, however, for physicists to obtain unambiguous experimental evidence of the existence of these exotic particles.

In April 2014, the LHCb Collaboration published measurements that demonstrated that the Z(4430)+ particle is composed of four quarks.

A year later, the LHCb physicists reported the observation of two pentaquarks, Pc(4450)+ and Pc(4380)+.

The LHCb team found the X(6900) tetraquark using the particle-hunting technique of looking for an excess of collision events, known as a ‘bump,’ over a smooth background of events.

Sifting through the full LHCb datasets from the first and second runs of the Large Hadron Collider, which took place from 2009 to 2013 and from 2015 to 2018 respectively, they detected a bump in the mass distribution of a pair of J/ψ particles, which consist of a charm quark and a charm antiquark.

The bump has a statistical significance of more than five standard deviations, the usual threshold for claiming the discovery of a new particle, and it corresponds to a mass at which particles composed of four charm quarks are predicted to exist.

References: R. Aaij, C. Abellán Beteta, T. Ackernley, B. Adeva, M. Adinolfi, H. Afsharnia, C.A. Aidala, S. Aiola, Z. Ajaltouni, S. Akar, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, G. Alkhazov, P. Alvarez Cartelle, A.A. Alves Jr, S. Amato, Y. Amhis, L. An, L. Anderlini, G. Andreassi, A. Andreianov, M. Andreotti, F. Archilli, A. Artamonov, M. Artuso, K. Arzymatov, E. Aslanides, M. Atzeni, B. Audurier, S. Bachmann, M. Bachmayer, J.J. Back, S. Baker, P. Baladron Rodriguez, V. Balagura, W. Baldini, J. Baptista Leite, R.J. Barlow, S. Barsuk, W. Barter, M. Bartolini, F. Baryshnikov, J.M. Basels, G. Bassi, V. Batozskaya, B. Batsukh, A. Battig, A. Bay, M. Becker, F. Bedeschi, I. Bediaga, A. Beiter, V. Belavin, S. Belin, V. Bellee, K. Belous, I. Belyaev, G. Bencivenni, E. Ben-Haim, A. Berezhnoy, R. Bernet, D. Berninghoff, H.C. Bernstein, C. Bertella, E. Bertholet, A. Bertolin, C. Betancourt, F. Betti, M.O. Bettler, Ia. Bezshyiko, S. Bhasin, J. Bhom, L. Bian, M.S. Bieker, S. Bifani, P. Billoir, M. Birch, F.C.R. Bishop, A. Bizzeti, M. Bjørn, M.P. Blago, T. Blake, F. Blanc, S. Blusk, D. Bobulska, V. Bocci, J.A. Boelhauve, O. Boente Garcia, T. Boettcher, A. Boldyrev, A. Bondar, N. Bondar, S. Borghi, M. Borisyak, M. Borsato, J.T. Borsuk et al., ‘Observation of structure in the J/ψ-pair mass spectrum LHCb collaboration’, arXiv: 2006.16957..

How Exactly Does Fever Help You Get Better? (Biology)

You’ve been dealing with sniffles and a sore throat for a day or so, hoping dearly that it’s just a minor bug, when bam! — you’re suddenly shivering, exhausted, and achy all over. You’ve got a fever. Before you go reaching for a fever-reducing drug, though, listen up: It might feel like death, but fever is often what your body needs to fight off that illness once and for all.

Fevers are such good infection fighters that species across the animal kingdom get them too. That includes everything from warm-blooded mammals like cats and dogs to cold-blooded species like lizards and fish, who move to a sunny rock or warmer water to raise their body temperature when they’re sick. But as common as they are, scientists haven’t known all that much about how fevers help you get better until recently.

The part that was best understood was how fevers start. When a virus or bacterium invades your cells, immune cells called macrophages come to your rescue by gobbling up the invader and cleaning up dead cells. They also let the rest of the body know what’s going down by sending out an alert via proteins called cytokines. These messengers travel up the body’s neural superhighway, known as the vagus nerve, making a beeline for both the brain’s pain center and the hypothalamus. That’s the brain region that controls not only temperature but hunger, thirst, sleepiness — all those other things that go haywire when you’re sick.

Once the hypothalamus knows the body is under attack, it sends out signals to stoke the fires of fever. But why? For a long time, people assumed that a higher body temperature makes it harder for bacteria and viruses to thrive, and eventually kills them off. That’s true, but it turns out to be a very small part of fever’s power.

Another soldier in the fight against infection is the lymphocyte or white blood cell. Once macrophages have begun battle, they present pieces of the invader proteins to T-lymphocytes, which use them to target and destroy infection. These cells get a big boost from toasty temperatures. In 2011, researchers found that when mice were injected with a virus then had their body temperatures raised by 2 degrees, their bodies produced more of a specific type of T-cell than those of the mice who stayed at a normal temperature.

In January, scientists got an even more detailed answer for why fever gives the immune system a boost: It helps more lymphocytes move to the area under attack. In order to get to their destination, lymphocytes have to move out of the lymph node, stick to the blood vessel, and then travel to the infection. Doing that sticking are molecules called integrins, which are expressed on the lymphocyte surface. Integrins are shaped kind of like balloons, with a large, sticky head and a skinny tail that burrows beneath the surface of the lymphocyte.

In a study published in the journal Immunity, researchers found that fever boosts an integrin-supercharging protein called heat shock protein 90 (Hsp 90) in T-lymphocytes. These bind to the integrin tail, sometimes two at a time, helping more integrins cluster on the surface of the lymphocyte and move it more efficiently to the area it’s needed most. The researchers found that this doesn’t just help T-lymphocytes, but all sorts of immune cells. Interestingly, Hsp-90 only kicked in at a temperature of 101.3 degrees Fahrenheit (38.5 degrees Celsius) — the kind of temp that would likely leave you bedridden for the day.

Fever is a valuable tool for keeping your body healthy, which is why you shouldn’t go too hard on the fever meds. Of course, if your fever is very high — 103 degrees Fahrenheit (39.4 Celsius) for adults, lower for children — you should consult a doctor, who may well tell you to take something to reduce it. But if not, maybe ride it out. Just know there’s a war going on inside you, and do what you can to help the good guys win.

References: (1) An article on, “The Immune System: Information about Lymphocytes, Dendritic Cells, Macrophages, and White Blood Cells”, Chemocare.

(2) Thomas A. Mace, Lingwen Zhong, Casey Kilpatrick, Evan Zynda, Chen-Ting Lee, Maegan Capitano, Hans Minderman, and Elizabeth A. Repasky, “Differentiation of CD8+ T cells into effector cells is enhanced by physiological range hyperthermia”, J Leukoc Biol. 2011 Nov; 90(5): 951–962, doi: 10.1189/jlb.0511229



(5) ChangDong Lin, YouHua Zhang, Kun Zhang, YaJuan Zheng, Ling Lu, HaiShuang Chang, Hui Yang, YanRong Yang, YaoYing Wan, ShiHui Wang, MengYa Yuan, ZhanJun Yan, RongGuang Zhang, YongNing He, GaoXiang Ge, Dianqing Wu, JianFeng Chen, “Fever Promotes T Lymphocyte Trafficking via a Thermal Sensory Pathway Involving Heat Shock Protein 90 and α4 Integrins”, VOLUME 50, ISSUE 1, P137-151.E6, JANUARY 15, 2019.

Colliding Star Destroys Supermassive Black Hole’s Corona in Distant Galaxy (Astronomy)

A team of astronomers has watched as an X-ray corona of a supermassive black hole in the active galactic nucleus 1ES 1927+654 was abruptly destroyed. The researchers think that their observations could be explained by the interaction between the accretion flow around the black hole and debris from a tidally disrupted star.

Fig: This two-panel illustration shows a black hole surrounded by a disk of gas, before and after the disk is partially dispersed. In the left panel, the ball of white light above the black hole is the black hole corona, a collection of ultra-hot gas particles that forms as gas from the disk falls into the black hole. The streak of debris falling toward the disk is what remains of a star that was torn apart by the black hole’s gravity. The right panel shows the black hole after the debris from the star has dispersed some of the gas in the disk, causing the corona to disappear. Image credit: NASA / JPL-Caltech.

In March 2018, an unexpected burst lit up the view of the All-Sky Automated Survey for Super-Novae (ASSASN), which surveys the entire night sky for supernova activity.

The survey observed that the brightness of 1ES 1927+654 jumped to about 40 times its normal luminosity.

Now, Dr. Kara, Dr. Ricci and their colleagues used multiple telescopes to observe 1ES 1927+654’s supermassive black hole in the X-ray, optical, and ultraviolet wave bands.

Most of these telescopes were pointed at the black hole periodically, for example recording observations for an entire day, every six months.

The researchers also watched the black hole daily with NASA’s Neutron Star Interior Composition Explorer (NICER).

With frequent observations, they were able to catch the black hole as it precipitously dropped in brightness, in virtually all the wave bands they measured, and especially in the high-energy X-ray band — an observation that signaled that the black hole’s corona had completely and suddenly vaporized.

Astrophysicists are unsure exactly what causes a corona to form, but they believe it has something to do with the configuration of magnetic field lines that run through a black hole’s accretion disk.

Closer in, and especially near the event horizon, material circles with more energy, in a way that may cause magnetic field lines to twist and break, then reconnect. This tangle of magnetic energy could spin up particles swirling close to the black hole, to the level of high-energy X-rays, forming the crown-like corona that encircles the black hole.

Dr. Kara and co-authors believe that if a wayward star was indeed the culprit in the corona’s disappearance, it would have first been shredded apart by the black hole’s gravitational pull, scattering stellar debris across the accretion disk.

This may have caused the temporary flash in brightness that ASSASN captured.

This tidal disruption would have triggered much of the material in the disk to suddenly fall into the black hole. It also might have thrown the disk’s magnetic field lines out of whack in a way that it could no longer generate and support a high-energy corona.

This last point is a potentially important one for understanding how coronas first form. Depending on the mass of a black hole, there is a certain radius within which a star will most certainly be pulled in by a black hole’s gravity.

The scientists calculated that if a star indeed was the cause of the black hole’s missing corona, and if a corona were to form in a supermassive black hole of similar size, it would do so within a radius of about 4 light minutes — a distance that roughly translates to about 75 million km from the black hole’s center.

The corona has since reformed, lighting up in high-energy X-rays which the team was also able to observe.

It’s not as bright as it once was, but the authors are continuing to monitor it, though less frequently, to see what more this system has in store.

Universe is 13.77 Billion Years Old (Astronomy)

Astronomers using NSF’s Atacama Cosmology Telescope (ACT) have taken a fresh look at the Cosmic Microwave Background (CMB), the oldest light in our Universe. Their new observations suggest that the Universe is 13.77 billion years old, give or take 40 million years. This estimate matches the one provided by the Standard Model of the Universe and measurements of the same light made by ESA’s Planck satellite.

Fig: This new picture of the Cosmic Microwave Background, the oldest light in the Universe, was taken by the Atacama Cosmology Telescope. This covers a swath of the sky 50 times as wide as the Moon, representing a region of space 20 billion light-years across. The light, emitted just 380,000 years after the Big Bang, varies in polarization (represented here by redder or bluer colors). Image credit: ACT Collaboration.

The age of the Universe also reveals how fast the cosmos is expanding, a number quantified by the Hubble constant.

The ACT measurements suggest a Hubble constant of 67.6 km per second per megaparsec (km/s/Mpc).

This result agrees almost exactly with the previous estimate of 67.4 km/s/Mpc by the Planck satellite team, but it’s slower than the 74 km/s/Mpc inferred from the measurements of galaxies.

References: (1) Simone Aiola et al. 2020. The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters. arXiv: 2007.07288. (2) Steve K. Choi et al. 2020. The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectra at 98 and 150 GHz. arXiv: 2007.07289 (3) Sigurd Naess et al. 2020. The Atacama Cosmology Telescope: arcminute-resolution maps of 18,000 square degrees of the microwave sky from ACT 2008-2018 data combined with Planck. arXiv: 2007.07290..

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)