From AAS NOVA: “Simulating a Plateauing Supernova”

From AAS NOVA

9.21.22
Kerry Hensley

The Hubble Space Telescope captured this image of a supernova shining in the outskirts of the galaxy NGC 2525. Supernova light curves have a variety of behaviors, which can tell us about the cause of the supernova as well as its surroundings. [NASA/ESA Hubble, A. Riess and the SH0ES team; Acknowledgment: Mahdi Zamani]

Supernovae show a wide variety of behaviors as they fade and these behaviors encode information about the exploding star and its surroundings. Can simulations help us understand why some supernovae maintain the same brightness for weeks or months?

Light Curve Characterization

The Pencil Nebula, located at the center image, is thought to be evidence of a shock wave created by a supernova. [ESO/Digitized Sky Survey 2; Acknowledgment: Davide De Martin; CC BY 4.0]

When massive stars end their lives as supernovae, researchers dissect their light curves to reconstruct the details of their demise. Some supernovae, known as Type IIP, hit a plateau after they begin to fade, sustaining the same brightness for weeks or months before starting to dim again. Modeling suggests that these supernovae get their characteristic brightness plateaus when the expanding shock wave heats and ionizes nearby gas, but more work is needed to understand the origin of this gas.

In a recent publication, Alexandra Kozyreva (Max Planck Institute for Astrophysics, Germany) and collaborators modeled supernova SN 2021yja to understand if its light curve can be explained by this emerging picture of Type IIP supernova evolution.

A comparison of the observed brightness of SN 2021yja (cyan circles) with modeled light curves for a model with (m15ni175; red) and without (m15 basic; black) circumstellar material. [Kozyreva et al. 2022]

Plateau Possibilities

Kozyreva and collaborators modeled SN 2021yja as a collapsing 15-solar-mass red supergiant — a star so large that it would engulf Mercury, Venus, Earth, and Mars if placed in our solar system. To test the impact of circumstellar gas on the exploding star’s light curve, the team compared models that incorporated a cloud of dense, hydrogen-rich material surrounding the star to those that didn’t. These simulations showed that circumstellar material is necessary to explain several features of SN 2021yja’s light curve, including its rapid rise and high peak brightness.

The best-fitting models incorporated 0.55 solar mass of surrounding material that extended from very close to the star’s surface out to 2,700 solar radii, and several facets of the model output indicated that this gas was distributed asymmetrically around the star. Given the density and proximity of the surrounding gas, the team found that the material was likely expelled in the span of just a few years. These results confirm that SN 2021yja fits the emerging picture of Type IIP supernovae, but they raise new questions about the source of the material in the star’s neighborhood.

Outflow Options

Kozyreva and coauthors outlined several possible sources for this material:

Stellar winds. Red supergiant stars produce vigorous stellar winds, but these winds typically expel material at a rate 100,000 times slower than necessary for stellar winds to explain the predicted amount of circumstellar material.

Binary interaction. If the star had a binary companion, the circumstellar material could have been generated by an enormous transfer of mass — large enough that it destabilizes the system and causes the stars to merge. However, this scenario likely causes less than one in 10,000 supernovae.

Convective behavior. The atmospheres of red supergiant stars undergo a slow churning motion called convection, which creates the conditions for gas in the star’s atmosphere to be lofted upwards and eventually lost. The gravitational tug of a binary companion could cause this mass loss to be asymmetrical.

The team suggested that convection in the star’s atmosphere is the most likely source of the gas surrounding SN 2021yja — and since convection is common in red supergiant stars, it may provide an explanation for the curious light curves of many Type IIP supernovae.

Citation

The Circumstellar Material around the Type IIP SN 2021yja, Alexandra Kozyreva et al 2022 ApJL 934 L31.

https://iopscience.iop.org/article/10.3847/2041-8213/ac835a

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “How (S)low Can You Go:: Pulsar Edition”

From AAS NOVA

9.16.22
Haley Wahl

An artist’s impression of an accreting neutron star. [Dana Berry/NASA Goddard Space Flight Center]

Pulsars are one of the most complex and mysterious objects in the universe; astronomers thought they had an answer to how and why pulsars lose energy and spin slower over time…but recent discoveries have made them rethink their current theories.

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at Mullard Radio Astronomy Observatory, University of Cambridge(UK), taken for the Daily Herald newspaper in 1968. Denied the Nobel.

An example of a pulsar in a supernova remnant; the Crab pulsar emits energy that lights up the Crab Nebula, both of which were formed in a supernova that occurred in the year 1054. [J. Hester and A. Loll (Arizona State University)/NASA/ESA]

A Lack of Long-Period Pulsars

Deep inside the gas and dust of some supernova remnants, you’ll find a pulsar: a neutron star with a magnetic fields 100 million times Earth’s and a density so high that a teaspoon of matter would weigh as much as Mount Everest.

Neutron Star L. Calçada/ European Southern Observatory [La Observatorio Europeo Austral] [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL)

Pulsars emit radio radiation and rotate rapidly; their spin periods generally fall between 2 milliseconds and 12 seconds. Puzzled by the lack of pulsars with rotation periods longer than 12 seconds, some astronomers have hypothesized that pulsars can no longer emit radio radiation when their rotation periods exceed a certain limit. Other researchers believe that our observing methods are biased toward pulsars with shorter periods.

However, recent discoveries of long-period pulsars with spin periods of 14 seconds, 23 seconds, and 76 seconds (and also a radio transient with a period of 1,091 seconds) have challenged these ideas and made astronomers rethink their models. How were these pulsars with long spin periods formed? A team led by Michele Ronchi at Spain’s Institute of Space Sciences and the Institute of Space Studies of Catalonia has proposed that it may have something to do with accretion from their parent supernovae.

The period and age of pulsars plotted for different initial magnetic field strengths and supernova disk fallback rates. [Ronchi et al. 2022]

The Low-Down on the Slow-Down

After their births in supernovae explosions, pulsars “spin down” over time as they lose energy through magnetic dipole radiation and their magnetic fields decay. However, it’s not clear that these processes alone can account for the few pulsars we see with very long spin periods. The team postulates that the long rotation periods seen in these pulsars might have been caused by material from the supernova falling back onto the neutron star and forming a disk, which will affect the spin rate of the pulsar. This would happen soon after a neutron star’s formation, and the amount of mass and the accretion rate would depend on the progenitor star’s mass and the dynamics of the supernova.

An example of the time evolution of the period of a pulsar. The two shaded boxes represent different phases of the accretion process. [Adapted from Ronchi et al. 2022]

Age Affects Accretion

The team performed simulations to understand how the spin period of a pulsar evolves over time, varying the initial magnetic field of the pulsar and the accretion rate to see if periods as long as 76 seconds are obtainable. They found that for newborn neutron stars with magnetic fields on the order of 1014–1015 G and moderate accretion rates, young long-period pulsars are possible. In neutron stars with lower initial magnetic fields, on the order of 1012 G, accretion from a fallback disk, if it is present, would have little effect. Therefore, the spin-down would be caused by magnetic dipole radiation alone, and the resulting pulsar’s period would be no longer than ~12 seconds.

Studying the mechanisms that lead to long-period pulsars could also help us understand other periodic transient events, like fast radio bursts. New radio surveys with powerful instruments such as the Low Frequency Array (LOFAR) and MeerKAT may find more of these long-period objects and put the team’s theories to the test.

Citation

Long-period Pulsars as Possible Outcomes of Supernova Fallback Accretion, Michele Ronchi et al 2022 ApJ 934 184.
https://iopscience.iop.org/article/10.3847/1538-4357/ac7cec/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “Beginnings of a Branch”

From AAS NOVA

9.14.22
Ben Cassese

The Sagittarius stellar stream wrapping around the Milky Way [David Law, UCLA]

The Sagittarius stellar stream is split into two branches: a large, bright river of stars and a smaller, fainter parallel creek. What’s the cause of this fissure, and where did the stars in this sibling stream come from?

A Stream of Stripped Stars

The Sagittarius (Sgr) dwarf galaxy has a complicated past with the Milky Way. The two galaxies have been slowly merging for several billion years, but the process has not gone smoothly for both parties. Although the Milky Way has been largely unaffected, many of Sgr’s original constituent stars have been stripped away and stretched into a long filament that wraps all the way around our sky. This is referred to as the Sagittarius stellar stream, and it was first discovered in the early 2000s.

For more than two decades now, astronomers have attempted to recreate the original conditions of this destructive embrace and envision what this contorted stream once looked like. Several models can reproduce the basic structure of the remains we see today, but the models that recreate the separation between bright and faint branches also make incorrect predictions about the spin of Sgr’s core. Now, a team led by Pierre-Antoine Oria (University of Strasbourg) has proposed a new origin for this faint branch that better matches our observations.

Disky Beginnings

To reach their conclusion, Oria and collaborators created a suite of artificial disks, each with their own inclination, angular momentum, and collection of massless test particles meant to represent stars. They then injected these disks into a previous model of the Sgr–Milky Way merger that did not reproduce the separation into different branches. After letting the simulation run, they checked which disk configuration best recreated the faint stream. Curiously, this best disk turned out to be nearly perpendicular to both the Milky Way’s plane and Sgr’s orbital plane.

The locations of selected test particles over the course of a simulation. Note the difference in scales between the top left panel and all other panels: this initial zoom shows that all particles that ended in the faint branch began nestled in initial spirals. [Oria et al. 2022]

After establishing that the faint branch stars likely came from this rotated disk, the team went a step further and determined not just the orientation of the parent disk but also the structure within it. By flagging particles that ended up in the faint branch at the end of the simulation, the team rewound the clock to check where those particles had begun their simulated lives. Although the authors had distributed the stars randomly throughout the initial disk without regard for any pattern, it turned out that all the stars that would someday arrive in the faint branch initially traced out a spiral structure.

New Ingredients

In summary, Oria and collaborators suggest that the stars that make up the faint branch of the Sgr stellar stream likely originated in a misaligned, spiraled disk. This model successfully reproduces today’s observed faint branch structure, but it is not without flaws: it over-predicts the thickness of the main branch and opens new questions about the origins of the spiral. Excitingly, though, the authors suggest that their disk can be added to a more complete model of the Sgr merger in the future, meaning this new ingredient brings us one step closer to a full reconstruction of Sgr and its slow destruction.

Citation

Revisiting a Disky Origin for the Faint Branch of the Sagittarius Stellar Stream, Pierre-Antoine Oria et al 2022 ApJL 932 L14.

https://iopscience.iop.org/article/10.3847/2041-8213/ac738c

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “A Software Solution for Tracking Down Gravitational Wave Sources”

From AAS NOVA

9.9.22
Kerry Hensley

Gravitational waves. Credit: W.Benger-Zib. MPG Institute for Gravitational Physics (DE)

An illustration of two neutron stars approaching a merger. [L. Calçada/The European Southern Observatory [La Observatorio Europeo Austral] [Observatoire européen austral][Europaiche Sûdsternwarte] (EU)(CL)]

When racing to follow up on a new detection of gravitational waves, every second of telescope time is precious. A recent publication describes how a new algorithm for scheduling observations might improve our ability to track down transient events.

Seeking Gravitational Wave Sources

Locations of the observatories that followed up on the detection of the gravitational wave signal GW170817. [LIGO-Virgo]

Caltech/MIT Advanced aLigo at Hanford, WA, Livingston, LA; and VIRGO Gravitational Wave interferometer, near Pisa(IT).

The search for the source of gravitational wave event GW170817 is an amazing success story. In the days following the initial detection, telescopes across the world pinpointed and monitored the resulting kilonova, leading to a deep understanding of the event — but since then, no other gravitational wave source has been definitively identified.

Searches for gravitational wave sources are challenging because the search areas are often large, telescope time is limited, and the events are transient. How can we track down the causes of gravitational wave signals in a way that makes the most efficient use of the available observing time? In a recent publication, B. Parazin (Northeastern University and University of Minnesota) put a new observation-scheduling algorithm to the test.

Scheduling Telescope Time

Parazin and collaborators tested a new algorithm optimized for the Zwicky Transient Facility (ZTF), which is designed to detect transient events.

Zwicky Transient Facility (ZTF) instrument installed on the 1.2m diameter Samuel Oschin Telescope at Palomar Observatory in California. Credit: Caltech Optical Observatories.

Caltech Palomar Samuel Oschin 48 inch Telescope, located in San Diego County, California, altitude 1712 m (5617 ft). Credit: Caltech.

The team aimed to maximize the odds of tracking down the source of a new gravitational wave signal while minimizing the amount of observing time needed. They also accounted for factors that are unique to the ZTF, such as the time needed to switch between filters.

In addition to the particulars of the ZTF observing setup, the algorithm takes as an input a map of the sky showing the probable locations of a gravitational wave source, which is released by gravitational wave observatories when a new signal is detected. From there, the algorithm identifies which out of the ZTF telescope’s 1,778 possible pointing directions are appropriate, groups pointings that are continuously observable during a selected length of time, and orders the pointings within each group so as to minimize the amount of time the telescope spends between observations.

Improving Efficiency

Comparison of the probability coverage of the existing algorithm in use by the ZTF (gwemopt) to that of the new algorithm introduced in this work (MUSHROOMS). The new algorithm performs better than the existing algorithm for cases located under the yellow line. [Parazin et al. 2022]

To compare the new algorithm to the one ZTF currently uses, the team scheduled observations with each method for 951 simulated detections of binary neutron star mergers. Under the conditions best suited to compare the two methods, Parazin and coauthors find that their new algorithm improves upon the existing software by 5.8%, on average — in other words, the new observing schedules increased the probability of finding the source. Since the existing algorithm sometimes outperformed the new algorithm, a hybrid approach — running both algorithms and choosing the more efficient solution — was the best, netting an average 8.1% improvement.

A final wrinkle is the fact that transient sources can fade rapidly, making the order in which the observations are carried out important — reach a source too late, and it may have dimmed beyond detection. When testing both algorithms on finding rapidly fading synthetic kilonovae, the team found that 1) once again, the hybrid approach had the best performance, and 2) the new algorithm had an advantage over the existing software when the search area was large.

Citation

Foraging with MUSHROOMS: A Mixed-integer Linear Programming Scheduler for Multimessenger Target of Opportunity Searches with the Zwicky Transient Facility, B. Parazin et al 2022 ApJ 935 87.
https://iopscience.iop.org/article/10.3847/1538-4357/ac7fa2/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “Simulations Suggest Magnetic Fields Made the First Stars Form Solo”

From AAS NOVA

9.7.22
Kerry Hensley

An artist’s impression of the first stars in the universe going supernova. [NAOJ]

The first stars in the universe, known as Population III stars, formed just a few hundred million years after the Big Bang. While researchers expect that most Population III stars led bright, brief lives, those with masses less than 0.8 solar mass would still be shining faintly today. Can magnetic fields in the early universe explain why we’ve yet to find these stars?

An infrared image of the Orion star-forming region with magnetic field lines measured by the Stratospheric Observatory for Infrared Astronomy traced on top. [D. Chuss, et al./NASA/SOFIA; M.McCaughrean, et al./ European Southern Observatory.]

National Aeronautics and Space Administration/DLR German Aerospace [Deutsches Zentrum für Luft- und Raumfahrt e.V.](DE)SOFIA airborne telescope and cameras.

Producing Population III Stars

There are many possible explanations for why low-mass Population III stars are so elusive, but the simplest explanation might be that they never existed at all. It’s challenging to prove that something doesn’t exist in the universe, but simulations give us a way to explore whether low-mass Population III stars could have formed in the conditions that existed when the first stars were born.

Previous research suggests that the early universe was suffused with a subtle magnetic field that was about a trillion times weaker than the fields measured in typical star-forming regions in the universe today. Magnetic fields play an important role in shaping — and sometimes suppressing — star formation in the local universe, leading researchers to wonder if the weak magnetic fields in the early universe could have halted the formation of low-mass stars entirely.

Simulation results for the unmagnetized case (top row) and the case in which the magnetic field strength was 10-20 Gauss (middle and bottom row). The top and middle rows show how the density of the gas varied between the two simulations at 0, 10, and 1,000 years of simulation time. The bottom row shows how the magnetic field strength was amplified and evolved over time in the magnetized case. [Hirano & Machida 2022]

Magnetic Magnification

Shingo Hirano (University of Tokyo and Kyushu University, Japan) and Masahiro Machida (Kyushu University, Japan) modeled the collapse of a cloud of gas under the conditions present in the early universe to understand how magnetic fields might have influenced the formation of the first stars.

The team performed magnetohydrodynamic simulations of a gas cloud with weak initial magnetic field strengths of 0, 10^-20, 10^-15, and 10^-10 Gauss. In the unmagnetized case, the cloud fragmented into a massive (~200 solar masses) central protostar and a handful of smaller protostars, all of which persisted until the end of the simulation at 1,000 years.

In the magnetized cases, on the other hand, the rapid rotation of the massive young star forming at the center of the cloud wound the magnetic field tighter and tighter, boosting the magnetic field strength up to 1,000 Gauss. The strong magnetic field prevented the cloud from fragmenting further, and the few small protostars that started to form dissipated entirely, leaving only the massive protostar at the end of the simulation. This result suggests that even a weak magnetic field can be amplified enough to stop small protostars from forming, meaning that the first stars may have all formed alone.

A Turbulent Twist

Hirano and Machida caution that while their simulations suggest that the magnetic fields in the early universe can prevent the formation of low-mass stars, other factors may influence the formation of the first stars; if the star-forming gas is turbulent, for example, it might be more inclined to fragment into multiple stars. Similarly, the slow process of diffusion could prevent the magnetic field from growing strong enough to play an important role.

In future work, the authors plan to introduce turbulence into their simulations, test the effects of different rotation rates of star-forming clouds, and extend the simulation out to 100,000 years. In the meantime, the search for Population III stars continues!

Citation

Exponentially Amplified Magnetic Field Eliminates Disk Fragmentation around Population III Protostars, Shingo Hirano and Masahiro N. Machida 2022 ApJL 935 L16.

https://iopscience.iop.org/article/10.3847/2041-8213/ac85e0/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “Where Do Eccentric Stellar Twins Come From?”

From AAS NOVA

9.2.22
Kerry Hensley

Hubble Space Telescope image of Alpha Centauri A and B. [NASA Goddard]

National Aeronautics and Space Administration/The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU) Hubble Space Telescope.

Binary Star Breakthroughs

By studying binary stars astronomers hope to discern the details of star formation as well as how repeated gravitational encounters can shape stellar systems after they’ve formed. Common though binary stars may be, they’re not without their mysteries, and recent data have revealed intriguing details about the binary stars in our galaxy.

One finding is that widely separated binary systems in which the stars have nearly the same mass — wide twin binaries — are more common than expected. Twin binaries are expected to form from a single disk of gas and dust, but these disks tend to be far smaller than the present-day separations of these systems.

If these distant binary companions formed close together in a single disk before being driven to their current locations by gravitational encounters, these systems should have extremely elongated, or eccentric, orbits — and thanks to the Gaia spacecraft, we can test that prediction for thousands of stars.

European Space Agency [La Agencia Espacial Europea][Agence spatiale européenne][Europäische Weltraumorganisation](EU) GAIA satellite.

Gaia Early Data Release 3.

Exploring Eccentricities

Widely separated binary systems take more than a thousand years to complete a single orbit, making it challenging to measure the eccentricity of an individual system. Instead, Hsiang-Chih Hwang (Princeton University) used a statistical technique to study nearly a million binary systems at once. Using stellar position and velocity data from Gaia, the team measured the angle between two vectors: one that describes the difference in the binary members’ motion across the sky (v) and one that connects the two stars (r).

By comparing the angle between those vectors to theoretical predictions for stellar populations with different eccentricities, the team determined that twin binaries with orbital separations of 400–1,000 au tend to have extremely eccentric orbits. Specifically, there appear to be a high number of systems with eccentricities between 0.95 and 1.0.

Formation Possibilities

This finding suggests that wide twin binaries likely form close together before being driven apart, but how these binary systems attain their eccentric orbits is still unclear. Hwang and collaborators explore several possibilities:

-An instantaneous “kick” could wrench a close circular orbit into a highly eccentric one, but it’s not clear what process could provide the kick.
-Wide, eccentric twin binary systems might instead have three stars, with the third star being a close, unresolved companion of one of the two widely separated stars. However, previous research suggests that unresolved stellar companions are not especially common among twin binaries.
-Interactions between a young binary system and the disk surrounding it could increase the system’s eccentricity. This process would affect all close binaries — not just twin binaries — but the results might be more apparent in the twin binary population because twins are more common among close binary systems.

The formation of wide, eccentric twin binaries has implications for single stars as well; Hwang and coauthors outline the possibility that the same process that drives close binary systems into highly eccentric orbits likely separates some systems entirely, creating pairs of “walkaway” stars that meander in opposite directions through the galaxy.

Citation

“Wide Twin Binaries are Extremely Eccentric: Evidence of Twin Binary Formation in Circumbinary Disks,” Hsiang-Chih Hwang et al 2022 ApJL 933 L32.
https://iopscience.iop.org/article/10.3847/2041-8213/ac7c70/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA and From The Weizmann Institute of Science מכון ויצמן למדע (IL): “Keeping Tabs on Clusters in an Ultra-Diffuse Galaxy”

From AAS NOVA

And

From The Weizmann Institute of Science מכון ויצמן למדע (IL)

8.31.22
Kerry Hensley

NGC 1052-DF2 is an example of an ultra-diffuse galaxy — one that lacks typical galaxy structures like spiral arms or a central bulge. NGC 1052-DF2 is missing most of its dark matter, but other ultra-diffuse galaxies might reside in massive dark-matter halos. [NASA, ESA, and P. van Dokkum (Yale University)]

Ultra-diffuse galaxies are the size of normal galaxies but far fainter, and many host an unusual abundance of globular clusters. A recent study takes a closer look at how one such galaxy’s globular clusters came to be where they are — and what this might tell us about the galaxy’s dark matter halo.

Copious Clusters

Observations over the past several years have given rise to numerous theories about the evolution of ultra-diffuse galaxies, and the arrangement of these galaxies’ globular clusters — spherical clusters containing hundreds of thousands of stars — can provide a useful test of these theories. Previous investigations of the ultra-diffuse galaxy NGC5846-UDG1, or UDG1, have shown that it has an exceptional collection of globular clusters for a galaxy of its size: researchers have found 54 candidate clusters, 11 of which have been spectroscopically confirmed.

UDG1’s population of globular clusters is also remarkable because its brightest clusters are concentrated near the center of the galaxy. The arrangement is unlikely to be random — what’s responsible for UDG1’s globular cluster distribution?

Influence of a Frictional Force

A team led by Nitsan Bar (Weizmann Institute of Science, Israel) hypothesized that the brightest and most massive globular clusters would naturally migrate to UDG1’s center because of gravitational dynamical friction. Dynamical friction isn’t the same as the friction that allows us to warm chilly hands by rubbing them together; instead, dynamical friction arises when objects interact gravitationally and lose a bit of their momentum in the process. In the case of UDG1, dynamical friction should cause the globular clusters to sink toward the galaxy’s center, and since the most massive clusters should experience the most friction, they should be found closest to the center.

To test this hypothesis, Bar and collaborators first used simple mathematical expressions to calculate where globular clusters with various masses would be located within UDG1 if dynamical friction is at work. Even without capturing the nuances of the system, these simple calculations matched observations fairly well, suggesting that dynamical friction plays an important role in UDG1.

A Test of Dark Matter Distributions

As a further test, the team performed detailed numerical simulations [done on personal laptops, e.g., M1-based MacBook Pro.], scattering globular clusters evenly throughout a UDG1-like galaxy and allowing them to drift for 10 billion years under the influence of dynamical friction, cluster mergers, and mass loss. These simulations showed that dynamical friction could have caused globular clusters to migrate to their current positions, likely from an initial arrangement slightly more dispersed than the current arrangement.

Bar and coauthors also explored the effects of changing the way mass is distributed in UDG1’s halo, which could give clues to the diffuse galaxy’s dark matter distribution. The team found that UDG1 could be situated in a massive dark matter halo, which would distinguish it from other ultra-diffuse galaxies that are almost entirely lacking in dark matter.

More work remains to be done, and the question of UDG1’s dark matter is not yet settled. The authors suggest new avenues for both theoretical and observational investigations: improved simulations of globular cluster formation can refine model results, and future data from Vera Rubin Observatory and the Nancy Grace Roman Space Telescope should illuminate the faintest globular clusters in ultra-diffuse galaxies.

Citation

“Dynamical Friction in Globular Cluster-rich Ultra-diffuse Galaxies: The Case of NGC5846-UDG1,” Nitsan Bar et al 2022 ApJL 932 L10.

https://iopscience.iop.org/article/10.3847/2041-8213/ac70df/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

The Weizmann Institute of Science מכון ויצמן למדע (IL) is one of the world’s leading multidisciplinary research institutions. Hundreds of scientists, laboratory technicians and research students working on its lushly landscaped campus embark daily on fascinating journeys into the unknown, seeking to improve our understanding of nature and our place within it.

Guiding these scientists is the spirit of inquiry so characteristic of the human race. It is this spirit that propelled humans upward along the evolutionary ladder, helping them reach their utmost heights. It prompted humankind to pursue agriculture, learn to build lodgings, invent writing, harness electricity to power emerging technologies, observe distant galaxies, design drugs to combat various diseases, develop new materials and decipher the genetic code embedded in all the plants and animals on Earth.

The quest to maintain this increasing momentum compels Weizmann Institute scientists to seek out places that have not yet been reached by the human mind. What awaits us in these places? No one has the answer to this question. But one thing is certain – the journey fired by curiosity will lead onward to a better future.

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “Probing a Bright Radio Galaxy with X-Rays”

From AAS NOVA

8.26.22
Haley Wahl

By now iconic image of Centaurus A from The European Southern Observatory(EU)/Wide Field Imager (Optical) ;MPG Institute for Radio Astronomy [MPG Institut für Radioastronomie](DE) A.Weiss et al. (Submillimetre) Atacama Pathfinder Experiment/; National Aeronautics Space Agency/NASA Chandra X-ray Space Telescope /R.Kraft et al. (X-ray)

Wide Field Imager on the 2.2 meter MPG/ESO telescope at Cerro LaSilla (CL)

MPG Institute for Astronomy [Max-Planck-Institut für Astronomie](DE)European Southern Observatory(EU) 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

ESO operates the Atacama Pathfinder Experiment, APEX, for The MPG Institute for Radio Astronomy [MPG Institut für Radioastronomie] (DE) at one of the highest observatory sites on Earth, at an elevation of 5100 metres, high on the Chajnantor plateau in Chile’s Atacama region.

The National Aeronautics and Space Administration Chandra X-ray telescope.

Deep inside the dust-shrouded core of radio galaxy Centaurus A, particles are being accelerated to relativistic speeds. What’s causing this acceleration, and what’s the nature of the matter around this energetic core? By using multiple telescopes to observe nearly the entire X-ray spectrum, astronomers may be getting closer to unlocking the answers.

Getting to the Core of the Mystery

Polarization, or the way the electromagnetic waves are oriented, is a powerful tool in astrophysics; the same concept that allows sunglasses to reduce glare can also be used to probe the emission mechanism of magnetized neutron stars and study the orientation of magnetic fields.

A diagram showing the concept of polarization; unpolarized light has electric fields going in all directions but polarized light has its electric field going in only one direction/vibrating in only one plane. Magnetic fields in space can change the orientation of the electric field, resulting in polarized light. [PhysicsOpenLab]

Measurements of the polarization properties of jets around the high-energy cores of supermassive black holes can help illuminate what type of physics is taking place, in particular how the high-energy emission is produced and how it behaves. These polarization measurements provide a valuable counterpart to other ways we probe the physics around black hole jets — like by examining how X-ray intensity varies with frequency.

Using simultaneous observations from multiple X-ray telescopes, a team led by Steven Ehlert at NASA’s Marshall Space Flight Center explores the polarization of the material and the X-ray spectrum around Centaurus A in order to better understand the material around the galaxy’s core. Centaurus A is of particular interest because it contains an active galactic nucleus — a black hole spewing radio jets into space — and it also emits X-rays. Though many studies have observed the X-ray emission from its core, we still haven’t pinpointed the source of this energetic light.

A Slew of X-Ray Telescope Observations

The team used the Imaging X-ray Polarimetry Explorer (IXPE) to observe polarized X-ray emission from Centaurus A.

The National Aeronautics and Space Agency/The Italian Space Agency A.S.I. [Agenzia Spaziale Italiana] (IT) IXPE spacecraft.

IXPE is a brand new mission dedicated to studying polarized X-ray emission from sources such as neutron stars and supermassive black holes. Launched in December 2021, the first science images from the mission were released this past February. The instrument measured low degrees of polarization in the core of Centaurus A, which suggests that the X-ray emission is coming from a scattering process rather than arising directly from the accelerated particles of the jet. The low degree of polarization, specifically near the core region, indicates that electrons are accelerated in an area around the core where the magnetic field lines are twisted and disordered.

An image of the core and surrounding regions of Centaurus A taken by IXPE. [Ehlert et al. 2022]

The spectrum of the source taken with the various telescopes, fit with a simple power law. [Ehlert et al. 2022]

By combining the IXPE measurements with simultaneous X-ray observations using the NuSTAR, Swift, and INTEGRAL telescopes, the team was able to observe Centaurus A throughout the full X-ray spectrum and see how the X-ray emission behaves from 0.3 keV all the way up to 400 keV.

National Aeronautics and Space Administration/Technical University of Denmark [Danmarks Tekniske Universite](DK)/ASI Italian Space Agency [Agenzia Spaziale Italiana](IT) NuSTAR X-ray telescope.

_________________________________________
National Aeronautics and Space Administration Neil Gehrels Swift spacecraft

National Aeronautics and Space Administration Neil Gehrels Swift X-ray, and UV/Visible light Observatory.

Burst Alert Telescope [BAT] Credit: swift.gsfc.nasa.gov

_________________________________________

European Space Agency [La Agencia Espacial Europea][Agence spatiale européenne][Europäische Weltraumorganisation](EU) Integral spacecraft.

They modeled the spectrum of the source and were able to fit a simple power law to it. The lack of complex spectral features indicates that the X-rays around Centaurus A are passing through an optically thin medium (material in space that the X-rays can pass through, where no scattering or absorption of the light takes place) that’s distant from where the X-rays originate.

A Unique Radio Galaxy?

This work, which is consistent with previous studies at other wavelengths, shows that the X-rays coming from Centaurus A’s core are produced by particles that are accelerated within about a light-year of the central black hole. Studying other galaxies that host luminous, accreting supermassive black holes will allow scientists to understand if the low degree of X-ray polarization is common, or if Centaurus A is unique among the population.
Citation

Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer, Steven R. Ehlert et al 2022 ApJ 935 116.
https://iopscience.iop.org/article/10.3847/1538-4357/ac8056/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “Can Machine Learning Warn Us of Approaching Geomagnetic Storms?”

From AAS NOVA

8.24.22
Kerry Hensley

This view of the swirling green aurora was captured from the International Space Station. [NASA]

Geomagnetic storms — disturbances in Earth’s protective magnetic shield caused by oncoming solar particles — can have real-world consequences. A recent research article explores how machine learning can be used to create an early warning system for these events.

Geomagnetic Storms on the Horizon

A white-light image of a coronal mass ejection taken by the Large Angle and Spectrometric Coronagraph. An extreme-ultraviolet image of the Sun is placed at the Sun’s location. [SOHO/LASCO, SOHO/EIT (ESA & NASA)]

SOHO Large Angle and Spectrometric Coronagraph. Credit: NASA/ESA

European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation]((EU)/National Aeronautics and Space Administration SOHO satellite. Launched in 1995.

A spacecraft at a distant vantage point glimpses a tangled mass of plasma and magnetic fields emerging from the Sun — a coronal mass ejection — headed our way. It’ll be hours or days before the coronal mass ejection collides with Earth, potentially disrupting radio communications, damaging spacecraft electronics, and threatening power grids. How can we predict if a coronal mass ejection will cause these disastrous consequences?

In a recent publication, a team led by Andreea-Clara Pricopi (Technical University of Cluj-Napoca, Romania) tested the ability of machine learning to predict whether a coronal mass ejection will disrupt Earth’s magnetic shield.

Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase.

This technique may provide a way to anticipate geomagnetic storms days in advance.

An Expansive Sample

Machine learning is a relatively new technique in which computers are trained on a set of inputs with known outcomes. The trained computer can then predict the outcomes of a fresh set of inputs.

Pricopi and collaborators took as inputs the speed, angle, and acceleration of coronal mass ejections identified in white-light images, as well as a measure of the overall solar flare activity. The corresponding output is a measure of how disrupted Earth’s magnetic field became, known as the disturbance storm time index. The team trained the model on these inputs and outputs for a subset of 24,403 coronal mass ejections observed between 1996 and 2014, 172 (0.7%) of which caused geomagnetic storms.

Artist’s impression of solar particles interacting with Earth’s protective magnetic shield, or magnetosphere, causing a geomagnetic storm. [NASA]

Because so few of the coronal mass ejections in the sample caused geomagnetic storms, Pricopi and collaborators had to be careful about assessing the model’s performance — after all, a model that simply labeled all 24,403 events as not causing a storm would be 99.3% accurate, but it would be useless as a predictor of geomagnetic storms! The team also wanted to be sure that their model correctly predicted all or most storms, even at the risk of false alarms, since the consequences of failing to prepare for a damaging geomagnetic storm are worse than preparing for a storm that never comes.

Prioritizing Powerful Events

Pricopi and coauthors trained their models on 80% of the data set, reserving the remaining 20% for testing the models’ performance. In order to push the models to prioritize finding geomagnetic storms, the team tested several strategies, including penalizing models that misclassified these events and creating synthetic storms based on real data to bulk up the sample size.

The best model correctly predicted about 80% of storms. The storms overlooked by the model tended to have poor quality data, and false alarms were most common for certain types of coronal mass ejections, giving clues as to how the model might be improved in the future.

These results show that machine learning can be used to predict geomagnetic storms days in advance using a limited number of inputs. However, the authors acknowledge that models that incorporate data from later in a coronal mass ejection’s evolution are more accurate. This suggests that the technique described in this work could be used to flag potentially damaging events, passing them to more precise models to get more information and improve our ability to prepare for an oncoming storm.

Citation

Predicting the Geoeffectiveness of CMEs Using Machine Learning, Andreea-Clara Pricopi et al 2022 ApJ 934 176.
https://iopscience.iop.org/article/10.3847/1538-4357/ac7962/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA: “Researchers Reveal a Hidden Pulsar”

From AAS NOVA

8.22.22
Kerry Hensley

The dense core of the globular cluster NGC 6397 is an excellent place to search for stellar remnants interacting with other objects. Credit: NASA, ESA, and T. Brown and S. Casertano (STScI)

Astronomers have discovered a second millisecond pulsar — a rapidly spinning, ultra-dense remnant of a massive star — in one of the nearest globular clusters to Earth. The new observations might help explain the surprising rarity of millisecond pulsars discovered in dense globular clusters.

Still image from an animation of a millisecond pulsar accreting material from its companion. [NASA]

Close Encounters of the Stellar Kind

In the cores of globular clusters, where gravitational encounters between stars are common, compact remnants of massive stars form binary systems with a wide range of properties. This sets the stage for the formation of millisecond pulsars: tiny, dense, rapidly spinning stellar remnants composed entirely of neutrons. All pulsars spin incredibly fast, but millisecond pulsars are the fastest of them all; if you stood on the equator of the speediest known millisecond pulsar, you’d whirl around at 24% of the speed of light. Astronomers believe that most millisecond pulsars started out as more slowly rotating solo acts, but after gaining a stellar companion, pulsars accrete matter and get spun up to “millisecond” status.

Nearby globular cluster NGC 6397 — a glittering, spherical collection of 400,000 stars — is home to a curious binary system that has been detected at X-ray, optical, and ultraviolet wavelengths. Its X-ray emission flashes with the period of the binary orbit, and optical observations show a red star at the same location. Previous research has suggested that this system contains a millisecond pulsar, but the characteristic radio pulses have been elusive.

In Pursuit of a Pulsar

In a new article, a team led by Lei Zhang (Chinese Academy of Sciences and Swinburne University of Technology, Australia) reports the results of their observations of the system made between 2019 and 2022 using the Parkes (Murriyang) radio telescope in Australia and the MeerKAT array in South Africa.

CSIRO-Commonwealth Scientific and Industrial Research Organization (AU) Parkes Observatory [Murriyang, the traditional Indigenous name], located 20 kilometres north of the town of Parkes, New South Wales, Australia, 414.80m above sea level.

SKA SARAO Meerkat Telescope (SA), 90 km outside the small Northern Cape town of Carnarvon, SA.

Zhang and collaborators discerned faint but detectable radio pulses every 5.8 milliseconds, and the pulses were modulated with a period of 1.97 days — the same period as the orbital period of the X-ray-emitting binary system at the same location.

This confirms that the system contains a millisecond pulsar, dubbed NGC 6397B, and further analysis of the timing of the pulses suggests that the pulsar is also the source of the X-ray emission detected previously.

Orbital period and companion mass for millisecond pulsars (MSPs) discovered in globular clusters (filled circles) and in the field (empty circles). The black and gray symbols indicate whether the companion is a white dwarf (WD), main-sequence star (MS), or an ultralight or planet-mass object (UL). [Zhang et al. 2022]

Implications of an Intermittent System

Even after the team tracked down the elusive pulsar, it still managed to give them the slip; the radio pulses became undetectable for 14 months before reemerging in early 2022. The system’s on-again off-again radio emission could point to one of two possibilities: hot, ionized gas flowing out from the companion star could be blocking the radio emission from reaching us when the binary system swings into certain orientations, or the act of accreting material from the companion star — the process that generates the X-rays — could temporarily halt the pulsar’s radio emission.

Previous research has suggested that pulsars in binary systems should be common in globular clusters with exceptionally dense cores, like NGC 6397, but most known pulsars in so-called core-collapse clusters are singletons. The particulars of the newly discovered system may provide an explanation as to why pulsar-hosting binary systems have been elusive in these environments: pulsars in binary systems might have faint or intermittent radio emission, making them hard to track down.

Citation

“Radio Detection of an Elusive Millisecond Pulsar in the Globular Cluster NGC 6397,” Lei Zhang et al 2022 ApJL 934 L21.
https://iopscience.iop.org/article/10.3847/2041-8213/ac81c3/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.