From Harvard-Smithsonian Center for Astrophysics(US): “The Distance to the North Polar Spur”

From Harvard-Smithsonian Center for Astrophysics(US)

An image of the Milky Way as seen at radio wavelengths and showing the prominent North Polar Spur, the larger Loop 1, and other features. Astronomers have measured the distance to the Spur from new Gaia satellite distances of molecular clouds and find that it is about five hundred light-years, much closer than proposed by some models that associated it with galactic nucleus and the Fermi bubbles. Credit: Haslam, C.G.T. et al., Astron. Astrophys. Suppl. Ser. 1982.

One of the largest structures in the Milky Way galaxy, the North Polar Spur, was discovered at radio and X-ray wavelengths. The Spur is a giant ridge of bright emission that rises roughly perpendicularly out of the plane of the galaxy starting roughly in the constellation of Sagittarius and then curves upward, stretching across the sky for over thirty degrees (the size of sixty full-moons) where it appears to join other bright filamentary features. The emitted radiation is highly polarized, indicative of its being produced by ionized gas in the presence of strong magnetic fields. Depending on how far away the Spur is from us, its length estimates range from hundreds to thousands of light-years.

One major theory for the Spur argues that it is a local structure produced by a supernova remnant and is perhaps only a few hundred light-years away. Other studies using the absorption of starlight seen through the Spur suggest it is more like a thousand light-years away. Using gas kinematic observations and related datasets, a different group argues that it is more like six-to-ten thousand light-years away. Because the general shape of the loop is reminiscent of the giant Fermi bubbles discovered emanating from the galactic center region, other astronomers argue that the Spur is actually part of a shock front produced by star formation activity that occurred about fifteen million years ago near the galactic center about twenty-five thousand light-years away.

Artist’s depiction of Fermi bubbles extending out of the Milky Way. Credit NASA Goddard Space Flight Center.

A robust constraint on the distance of the Spur has implications for our understanding of its origin and structure, but as well for that of other bright extended emission loops, the galactic bubbles, supernova activities in the solar neighborhood, and outflows of material seen coming from nuclei in other galaxies. CfA astronomers Catherine Zucker, Joshua Speagle, and Alyssa Goodman and their colleagues used the recent release of Gaia mission parallax measurements to determine accurate and precise distances to local molecular clouds. By comparing those data with measurements of the interstellar extinction toward the Spur and independent observations of the quantities of gas along different lines-of-sight, they conclude that almost all of the Spur is within a distance of five hundred light-years (a smaller section might be as far as a few thousand light-years). Based on their results, they argue that the Spur is not associated with the Fermi bubbles nor the galactic center, but rather with the closer Scorpius-Centaurus OB association of massive young stars.

Science paper:
Constraining the distance to the North Polar Spur with Gaia DR2
MNRAS

See the full article here .

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The Harvard-Smithsonian Center for Astrophysics(US) combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Comet or Asteroid- What Killed the Dinosaurs And Where Did it Come From?”

From Harvard-Smithsonian Center for Astrophysics

February 15, 2021

Nadia Whitehead
Public Affairs Officer
Center for Astrophysics | Harvard & Smithsonian
nadia.whitehead@cfa.harvard.edu
617-721-7371

An artist’s impression of what the Chicxulub crater might have looked like soon after an asteroid struck the Yucatán Peninsula in Mexico. Researchers studied the peak rings, or circular hills, inside the crater. Credit: Detlev van Ravenswaay/Science Source.

The Chicxulub impactor, as it’s known, left behind a crater off the coast of Mexico that spans 93 miles and runs 12 miles deep. Its devastating impact brought the reign of the dinosaurs to an abrupt and calamitous end by triggering their sudden mass extinction, along with the end of almost three-quarters of the plant and animal species living on Earth.

The enduring puzzle: Where did the asteroid or comet originate, and how did it come to strike Earth? Now, a pair of researchers at the Center for Astrophysics | Harvard & Smithsonian believe they have the answer.

In a study published today in Nature’s Scientific Reports, Harvard University astrophysics undergraduate student Amir Siraj and astronomer Avi Loeb put forth a new theory that could explain the origin and journey of this catastrophic object.

Using statistical analysis and gravitational simulations, Siraj and Loeb calculate that a significant fraction of long-period comets originating from the Oort cloud, an icy sphere of debris at the edge of the solar system, can be bumped off-course by Jupiter’s gravitational field during orbit.

Kuiper Belt and Oort Cloud. Credit: NASA.

“The solar system acts as a kind of pinball machine,” explains Siraj, who is pursuing bachelor’s and master’s degrees in astrophysics, in addition to a master’s degree in piano performance at the New England Conservatory of Music. “Jupiter, the most massive planet, kicks incoming long-period comets into orbits that bring them very close to the sun.”

During close passage to the sun, the comets — nicknamed “sungrazers” — can experience powerful tidal forces that break apart pieces of the rock and ultimately, produce cometary shrapnel.

“In a sungrazing event, the portion of the comet closer to the sun feels a stronger gravitational pull than the part that is further, resulting in a tidal force across the object,” Siraj says. “You can get what’s called a tidal disruption event, in which a large comet breaks up into many smaller pieces. And crucially, on the journey back to the Oort cloud, there’s an enhanced probability that one of these fragments hit the Earth.”

The new calculations from Siraj and Loeb’s theory increase the chances of long-period comets impacting Earth by a factor of about 10, and show that about 20 percent of long-period comets become sungrazers.

The pair say that their new rate of impact is consistent with the age of Chicxulub, providing a satisfactory explanation for its origin and other impactors like it.

“Our paper provides a basis for explaining the occurrence of this event,” Loeb says. “We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs.”

Evidence found at the Chicxulub crater suggests the rock was composed of carbonaceous chondrite. Siraj and Loeb’s hypothesis might also explain this unusual composition.

A popular theory on the origin of Chicxulub claims that the impactor originated from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. However, carbonaceous chondrites are rare amongst main-belt asteroids, but possibly widespread amongst long-period comets, providing additional support to the cometary impact hypothesis.

Other similar craters display the same composition. This includes an object that hit about 2 billion years ago and left the Vredefort crater in South Africa, which is the largest confirmed crater in Earth’s history, and the impactor that left the Zhamanshin crater in Kazakhstan, which is the largest confirmed crater within the last million years. The researchers say that the timing of these impacts support their calculations on the expected rate of Chicxulub-sized tidally disrupted comets.

Siraj and Loeb say their hypothesis can be tested by further studying these craters, others like them, and even ones on the surface of the moon to determine the composition of the impactors. Space missions sampling comets can also help.

Aside from composition of comets, the new Vera Rubin Observatory in Chile may be able to observe tidal disruption of long-period comets after it becomes operational next year.

NOIRLab Vera C. Rubin Observatory Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes, altitude 2,715 m (8,907 ft).

“We should see smaller fragments coming to Earth more frequently from the Oort cloud,” Loeb says. “I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments.”

Loeb says understanding this is not just crucial to solving a mystery of Earth’s history but could prove pivotal if such an event were to threaten the planet.

“It must have been an amazing sight, but we don’t want to see that again,” he said.

See the full article here.

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics via phys.org: “Rare blast’s remains discovered in Milky Way’s center”

From Harvard-Smithsonian Center for Astrophysics

via

phys.org

This composite image of X-ray data from Chandra (blue) and radio emission from the Very Large Array (red) contains the first evidence for a rare type of supernova in the Milky Way. By analyzing over 35 days’ worth of Chandra observations, researchers found an unusual pattern of elements such as iron and nickel in the stellar debris. The leading explanation is that this supernova remnant, called Sgr A East, was generated by a so-called Type Iax supernova. This is a special class of Type Ia supernova explosions that are used to accurately measure distances across space and study the expansion of the Universe. Credit: X-ray: NASA/CXC/Nanjing Univ./P. Zhou et al. Radio: NSF/NRAO/VLA.

NASA Chandra X-ray Space Telescope.

NRAO Karl G Jansky Very Large Array, located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes.

Astronomers may have found our galaxy’s first example of an unusual kind of stellar explosion. This discovery, made with NASA’s Chandra X-ray Observatory, adds to the understanding of how some stars shatter and seed the universe with elements critical for life on Earth.

This intriguing object, located near the center of the Milky Way, is a supernova remnant called Sagittarius A East, or Sgr A East for short. Based on Chandra data, astronomers previously classified the object as the remains of a massive star that exploded as a supernova, one of many kinds of exploded stars that scientists have cataloged.

Using longer Chandra observations, a team of astronomers has now instead concluded that the object is left over from a different type of supernova. It is the explosion of a white dwarf, a shrunken stellar ember from a fuel-depleted star like our Sun. When a white dwarf pulls too much material from a companion star or merges with another white dwarf, the white dwarf is destroyed, accompanied by a stunning flash of light.

Astronomers use these “Type Ia supernovae” because most of them mete out almost the same amount of light every time no matter where they are located. This allows scientists to use them to accurately measure distances across space and study the expansion of the universe.

Quick Look: Sagittarius A East.

Data from Chandra have revealed that Sgr A East, however, did not come from an ordinary Type Ia. Instead, it appears that it belongs to a special group of supernovae that produce different relative amounts of elements than traditional Type Ias do, and less powerful explosions. This subset is referred to as “Type Iax,” a potentially important member of the supernova family.

“While we’ve found Type Iax supernovae in other galaxies, we haven’t identified evidence for one in the Milky Way until now,” said Ping Zhou of Nanjing University in China, who led the new study while at the University of Amsterdam. “This discovery is important for getting a handle of the myriad ways white dwarfs explode.”

The explosions of white dwarfs is one of the most important sources in the universe of elements like iron, nickel, and chromium. The only place that scientists know these elements can be created is inside the nuclear furnace of stars or when they explode.

“This result shows us the diversity of types and causes of white dwarf explosions, and the different ways that they make these essential elements,” said co-author Shing-Chi Leung of Caltech in Pasadena, California. “If we’re right about the identity of this supernova’s remains, it would be the nearest known example to Earth.”

Astronomers are still debating the cause of Type Iax supernova explosions, but the leading theory is that they involve thermonuclear reactions that travel much more slowly through the star than in Type Ia supernovae. This relatively slow walk of the blast leads to weaker explosions and, hence, different amounts of elements produced in the explosion. It is also possible that part of the white dwarf is left behind.

Sgr A East is located very close to Sagittarius A*, the supermassive black hole in the center of our Milky Way galaxy, and likely intersects with the disk of material surrounding the black hole. The team was able to use Chandra observations targeting the supermassive black hole and the region around it for a total of about 35 days to study Sgr A East and find the unusual pattern of elements in the X-ray data. The Chandra results agree with computer models predicting a white dwarf that has undergone slow-moving nuclear reactions, making it a strong candidate for a Type Iax supernova remnant.

“This supernova remnant is in the background of many Chandra images of our galaxy’s supermassive black hole taken over the last 20 years,” said Zhiyuan Li, also of Nanjing University. “We finally may have worked out what this object is and how it came to be.”

In other galaxies, scientists observe that Type Iax supernovae occur at a rate that is about one third that of Type Ia supernovae. In the Milky Way, there have been three confirmed Type Ia supernova remnants and two candidates that are younger than 2,000 years, corresponding to an age when remnants are still relatively bright before fading later. If Sgr A East is younger than 2,000 years and resulted from a Type Iax supernova, this study suggests that our galaxy is in alignment with respect to the relative numbers of Type Iax supernovae seen in other galaxies.

Along with the suggestion that Sgr A East is the remnant from the collapse of a massive star, previous studies have also pointed out that a normal Type Ia supernova had not been ruled out. The latest study conducted with this deep Chandra data argue against both the massive star and the normal Type Ia interpretations.

These results will be published on Wednesday February 10th, 2021 in The Astrophysical Journal.

See the full article here .

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “X-Ray Emission from Dark Matter”

From Harvard-Smithsonian Center for Astrophysics

A composite image of a galaxy cluster [Bullet Cluster NASA Chandra NASA ESA Hubble, evidence of shock.] formed from the collision of two large clusters of galaxies. Hot X-ray emitting gas is shown in pink and dark matter (inferred from its gravitational influence) is shown in blue. Astronomers have used archival Chandra X-ray data to constrain the possibility that the mysterious dark matter in the universe is made of sterile neutrinos.
Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.)

NASA Chandra X-ray Space Telescope.

NASA/ESA Hubble Telescope.

Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high.

Wide Field Imager on the 2.2 meter MPG/ESO telescope at Cerro LaSilla.

MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

About eighty-five percent of the matter in the cosmos emits neither light nor any other known kind of radiation as far as is known, and hence is called Dark Matter. One of its other notable qualities is that it only interacts with other matter via gravity; it carries no electromagnetic charge, for example. Dark matter is also called “dark” because it is mysterious. It is not composed of atoms or their usual constituents (like electrons and protons) or of any other kind of known elementary particle.

Because dark matter is by far the dominant component of matter in the universe, its distribution and gravity have profoundly influenced the evolution of galactic structures as well as the distribution of the cosmic microwave background radiation.

Cosmic microwave background radiation. Stephen Hawking Center for Theoretical Cosmology U, Cambridge (UK).

Indeed, the remarkable agreement between the values of key cosmic parameters (like the universe’s rate of expansion) derived independently from two completely different cosmic structures, galaxies and the microwave background, lend credence to big bang models that require an important role for dark matter.

Physicists have tried to imagine new kinds of particles consistent with the known laws of the universe to explain dark matter, but so far none have been confirmed. One tantalizing possibility for a new particle is the so-called “sterile neutrino.” There are currently three known types of neutrinos. All of them interact with matter via gravity and via the weak force (the weakest of the four forces of nature). All were originally thought to have no mass, like the photon, but about twenty years ago physicists discovered that they do have slight masses – about a million times less than an electron’s mass but still enough to pose a fatal problem for physics’ so-called Standard Model of particles.

Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS).

A possible solution would be the existence of a more massive neutrino, perhaps a thousand times bigger, dubbed the “sterile neutrino” because it would not interact via the weak force. It has never been detected.

Astronomers realized that if dark matter were composed of sterile neutrinos, then when these particles occasionally decayed they could emit a detectable X-ray photon. About seven years ago, X-ray astronomers reported finding a strange, faint X-ray spectral emission feature coming from clusters of galaxies where dark matter was prevalent. They suggested this feature could be the signature of the sterile neutrino. In subsequent years there have been many attempts to confirm the detection or to attribute it to instrumental or other non-astronomical effects, with only mixed successes. CfA astronomers Esra Bulbul and Francesca Civano and their colleagues have now completed an extensive archival study of Chandra X-Ray Observatory data, searching for this elusive feature. They did not find it, but their new analysis, consistent with other recently published limits, more heavily constrains the possible decay character of the putative sterile neutrino by as much as a factor of two under some assumptions, but cannot rule it out entirely.

Science paper:
Probing the Milky Way’s Dark Matter Halo for the 3.5keV Line
The Astrophysical Journal

Dark Matter Background
Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, some 30 years later, did most of the work on Dark Matter.

Fritz Zwicky from http:// palomarskies.blogspot.com.

Coma cluster via NASA/ESA Hubble.

In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).

Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL).

Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu.

See the full article here .

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Please help promote STEM in your local schools.

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Astronomers Discover First Cloudless Jupiter-Like Planet”

From Harvard-Smithsonian Center for Astrophysics

January 22, 2021
Nadia Whitehead
Public Affairs Officer
Center for Astrophysics | Harvard & Smithsonian
nadia.whitehead@cfa.harvard.edu

Artist illustration of exoplanet WASP-62b. The illustration is drawn from the perspective of an observer nearby to the planet. Credit: M. Weiss/Center for Astrophysics | Harvard & Smithsonian.

Astronomers at the Center for Astrophysics | Harvard & Smithsonian have detected the first Jupiter-like planet without clouds or haze in its observable atmosphere. The findings were published this month in The Astrophysical Journal Letters.

Named WASP-62b, the gas giant was first detected in 2012 [MNRAS] through the Wide Angle Search for Planets (WASP) South survey. Its atmosphere, however, had never been closely studied until now.

“For my thesis, I have been working on exoplanet characterization,” says Munazza Alam, a graduate student at the Center for Astrophysics who led the study. “I take discovered planets and I follow up on them to characterize their atmospheres.”

Known as a “hot Jupiter,” WASP-62b is 575 light years away and about half the mass of our solar system’s Jupiter. However, unlike our Jupiter, which takes nearly 12 years to orbit the sun, WASP-62b completes a rotation around its star in just four-and-a-half days. This proximity to the star makes it extremely hot, hence the name “hot Jupiter.”

Using the Hubble Space Telescope, Alam recorded data and observations of the planet using spectroscopy, the study of electromagnetic radiation to help detect chemical elements. Alam specifically monitored WASP-62b as it swept in front of its host star three times, making visible light observations, which can detect the presence of sodium and potassium in a planet’s atmosphere.

“I’ll admit that at first I wasn’t too excited about this planet,” Alam says. “But once I started to take a look at the data, I got excited.”

While there was no evidence of potassium, sodium’s presence was strikingly clear. The team was able to view the full sodium absorption lines in their data, or its complete fingerprint. Clouds or haze in the atmosphere would obscure the complete signature of sodium, Alam explains, and astronomers usually can only make out small hints of its presence.

“This is smoking gun evidence that we are seeing a clear atmosphere,” she says.

Cloud-free planets are exceedingly rare; astronomers estimate that less than 7 percent of exoplanets have clear atmospheres, according to recent research [RNAAS]. For example, the first and only other known exoplanet with a clear atmosphere was discovered in 2018 [Nature]. Named WASP-96b, it is classified as a hot Saturn.

Astronomers believe studying exoplanets with cloudless atmospheres can lead to a better understanding of how they were formed. Their rarity “suggests something else is going on or they formed in a different way than most planets,” Alam says. Clear atmospheres also make it easier to study the chemical composition of planets, which can help identify what a planet is made of.

With the launch of the James Webb Space Telescope later this year, the team hopes to have new opportunities to study and better understand WASP-62b. The telescope’s improved technologies, like higher resolution and better precision, should help them probe the atmosphere even closer to search for the presence of more elements, such as silicon.

See the full article here .

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Please help promote STEM in your local schools.

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “An Earth-like Stellar Wind for Proxima Centauri c”

From Harvard-Smithsonian Center for Astrophysics

November 27, 2020

An optical image of the starfield near Proxima Cen. The two bright stars are (left) Alpha and (right) Beta Centauri. Proxima Centauri, the closest star to the Sun, is the faint red dot inside the red circle. A second planet, Proxima c, was recently discovered orbiting Proxima Cen every 5.3 years. Astronomers calculating the likely effects of the star’s wind on the planet conclude that a possible atmosphere would experience Earth-like conditions. Credit: Skatebiker.

Proxima Centauri is the closest star to the Sun, and its planet, Proxima Cen b (“Proxima b”), lies in its habitable zone (the distance range within which surface water can be liquid), making the planet a prime target for exoplanet characterization. The star is an M- dwarf with a mass of only 0.12 solar-masses and an effective surface temperature of about 3000 kelvin. The comparatively low surface temperature means that its habitable zone lies very close to the star and Proxima b, with its mass of about 1.2 Earth-masses, lies about twenty times closer to the star than the Earth does to the Sun, orbiting in only 11.2 days. Being as close as it is to its star, Proxima b (like all habitable-zone exoplanets around M-dwarf stars) is susceptible to stellar flares, winds, X-rays, and other kinds of activity that could disrupt its atmosphere and possibilities for life. These activities are linked to the strong magnetic fields in M-dwarfs, and they remain active in dwarf stars over much longer timescales than in higher-mass stars like the Sun, so that the cumulative exposures are commensurately greater. All these issues have been investigated in some detail for Proxima b; one conclusion, for example, is that it is probably subject to wind pressures ten thousand times larger than those exerted bu the Sun on the Earth.

A new planet has recently been discovered in the Proxima Cen system, Proxima c, after astronomers spotted slight variations in the orbital velocity of Proxima b (because it does not transit the star, its discovery was made by monitoring its velocity, not the star’s lightcurve). Followup studies of Proxima c determined that it was a ~ six Earth-mass planet and orbited at 1.44 AU every 5.3 years – and is much farther away from the star than Proxima b. (There are even hints of the presence of a third planet). CfA astronomers Jeremy Drake and Cecilia Garraffo, and their colleagues, investigated the effects the star’s activity might have on Proxima c’s atmosphere.

The scientists constructed the most comprehensive numerical simulation of the space environment of the Proxima Cen system that has been done to date including models for the stellar corona and realistic surface magnetic field configurations during the minimum and maximum activity states of the star. Their results indicate that Proxima c experiences Earth-like conditions, at least in terms of stellar wind effects. It is not known whether or not Proxima c actually has an atmosphere, but the new models indicate the conditions are not unduly corrosive and are favorable for the persistence of any atmosphere that does exist.

Science paper:
An Earth-like Stellar Wind Environment for Proxima Centauri c
The Astrophysical Journal

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “‘Strange Rays’ Crowd Sourced on Social Media Shed Light on Black Hole Illumination”

From Harvard-Smithsonian Center for Astrophysics

November 19, 2020

Amy Oliver
Public Affairs
Center for Astrophysics | Harvard & Smithsonian
Fred Lawrence Whipple Observatory
520-879-4406
amy.oliver@cfa.harvard.edu

Judy Schmidt, an image processing expert and citizen scientist, processed this image of IC5063–a Seyfert galaxy with an active galactic nuclei–from Barth’s Prop15444 and discovered what looked like dark shadows or cones pointing inward towards the center of the galaxy. Credit: NASA/ESA/A. Barth/J. Schmidt.

Sparked by an image uploaded to Twitter, new research indicates that the light produced by black hole accretion may be bright enough to reflect off of dust, illuminating the host galaxy, and creating light and dark rays similar to the effect of crepuscular rays on Earth. The research is published in The Astrophysical Journal Letters.

When a supermassive black hole accretes, or “feeds,” on the matter surrounding it, the resulting release of energy gives off an intense light. Until now, scientists believed that this light only illuminates the parts of a galaxy that fall within narrow ionization cones. But photographic evidence of IC 5063—a radio-loud Seyfert galaxy with an active galactic nucleus (AGN)—indicates that the light, or rays—which scientists liken to the crepuscular rays cast by clouds that obscure the sun near sunset—may be bright enough to reflect off of nearby dust, illuminating most of the galaxy, causing shadows from the black hole ring, or dark rays, in between.

“We think we’ve found evidence that there is probably dust all over the galaxy scattering light from the accreting black hole in the galaxy’s active nucleus, and that the light can illuminate almost the whole galaxy,” said Peter Maksym, an astronomer at the Center for Astrophysics | Harvard & Smithsonian and lead author on the study. “We know that this galaxy recently had a merger with another galaxy and that could kick up dust everywhere. It’s also possible that the black hole jets are kicking up dust from near the nucleus.”

Using images from the Hubble Space Telescope, the team focused in on IC 5063 and its torus—an unseen ring of cool, dusty gas surrounding the black hole—which might be the source of the light and its rays.

“The discovery shows that the torus, or ring, could be very thin—light seems to get out almost everywhere. If the torus is big enough it becomes unstable, the gravity and rotation holding it together point one direction near the black hole and in a different direction as influences from the galaxy start to become important. This looks like a warp or a bend,” said Maksym. “It’s possible that the warping creates big enough gaps for some of the light to shine through, and as the torus rotates, beams of light could sweep through across the galaxy like a lighthouse beams through fog. Scientifically, it’s showing us something that is hard, and usually impossible, to see directly. This could have implications for anybody trying to understand the behavior of supermassive black holes and their environments.”

Unlike most scientific research, the team observing IC 5063’s strange rays assembled in a peculiar fashion: via crowd sourcing on social media. In December 2019, space image processing expert and citizen scientist Judy Schmidt noticed strange cones while processing an image of IC 5063, at first wondering if they were real, and if they were, whether they were galaxy-sized shadows, star streams, or something else.

“I noticed the dark rays almost immediately after I’d opened the file in Photoshop and began working to enhance them to make sure what I thought I saw was there. I couldn’t see them in the archive thumbnails or the preview of the stretched image in FITS Liberator,” said Schmidt, adding that when she first saw what appeared to be shadows, she thought, “That’s not possible is it?” In her earliest tweets about the phenomena, Schmidt asked her followers, “Are these cones I’m straining to see real?” and “What are they? This is an active galaxy with a supermassive black hole in the middle. Is it casting galaxy-sized shadows? Or are those just star streams?”

It didn’t take long for Maksym and other scientists to notice the tweet and start making conjectures, which eventually led to the formation of the research team and the discovery.

“Judy has a keen eye for what looks weird, which, as in this case, can have important scientific implications. In December, she noticed some ‘dark rays’ extending from the nucleus of the galaxy IC 5063 and Tweeted to her followers asking if they might be anything interesting,” said Maksym, whose interest was immediately piqued since he was already working on the same galaxy from a different scientific angle. “Several of us chimed in and started speculating what could be causing the rays, and we really had no idea at first. When you read the Twitter thread, you can see how the ideas unfolded in real-time, and transformed into this really unusual research.”

The discovery is still new, and scientists don’t have all of the answers about the dust and its existence, or what’s really causing the dark rays; it has instead, opened an entirely new line of study and questions for scientists to ponder. “We don’t 100-percent know what’s going on; this whole discovery was unexpected,” said Maksym. “Next, other scientists will test our conclusions with new observations and modeling, and we will start exploring other ways to look at IC 5063, in other wavebands, and with other instruments. This is a project that is just begging for new data because it raises more questions than it answers.”

See the full article here .

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Please help promote STEM in your local schools.

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “The First Habitable-Zone, Earth-sized Planet Discovered with TESS”

From Harvard-Smithsonian Center for Astrophysics

A schematic of the planets around the nearby M dwarf star TOI-700, discovered by TESS. The third (the farthest planet from the star), TOI-700d, lies within the star’s habitable zone (shown in green). Using the IRAC camera on Spitzer, the team refined the planet’s mass as 2.1 Earth-masses and 1.14 Earth-radii. (The scale shows 0.2 astronomical units; AU being the average Earth-Sun distance.) Credit: Rodriguez et al 2020.

TESS, the Transiting Exoplanet Survey Satellite, was launched in 2018 with the goal of discovering small planets around the Sun’s nearest neighbors, stars bright enough to allow for follow-up characterizations of their planets’ masses and atmospheres.

NASA/MIT TESS replaced Kepler in search for exoplanets.

TESS has so far discovered seventeen small planets around eleven nearby stars that are M dwarfs — stars that are smaller than the Sun (less than about 60% of the Sun’s mass) and cooler (surface temperatures less than about 3900 kelvin). In a series of three papers that appeared together this month, astronomers report that one of these planets, TOI-700d, is Earth-sized and also located in its star’s habitable zone; they also discuss its possible climate.

CfA astronomers Joseph Rodriguez, Laura Kreidberg, Karen Collins, Samuel Quinn, Dave Latham, Ryan Cloutier, Jennifer Winters, Jason Eastman, and David Charbonneau were on the teams that studied TOI-700d, one of three small planets orbiting one M dwarf star (its mass is 0.415 solar masses) located one hundred and two light-years from Earth. The TESS data analysis found the tentative sizes of the planets as being approximately Earth-sized, 1.04, 2.65 and 1.14 Earth-radii, respectively, and their orbital periods as 9.98, 16.05, and 37.42 days, respectively. In our solar system, Mercury orbits the Sun in about 88 days; it is so close to the Sun that its temperature can reach over 400 Celsius. But because this M-dwarf star is comparatively cool the orbit of its third planet, even though much closer to the star than Mercury is to the Sun, places it in the habitable zone – the region within which the temperatures allow surface water (if any) to remain liquid when there is also an atmosphere. That makes this Earth-sized planet TOI-700d particularly interesting as a potential host for life.

The TESS detections were exciting but uncertain: the signals were faint and a small possibility remained that the TOI-700d detection was spurious. Because of the potential importance of finding a nearby Earth-sized planet in a habitable zone, the TESS scientists turned to the IRAC camera on the Spitzer Space Observatory for confirmation.

IRAC camera on the Spitzer space telescope.

NASA/Spitzer Infrared telescope no longer in service. Launched in 2003 and retired on 30 January 2020. Credit: NASA.

Before being turned off by NASA in February 2020, the IRAC camera was by far the most sensitive near infrared camera in space. The TESS team observed TOI-700 with IRAC in October of 2019 and January of 2020, acquiring clear detections of the planets with about twice the signal-to-noise of TESS, enough to give a 61% improvement in the planet’s orbit and to significantly refine our knowledge of its other characteristics, refining the radius as above and finding the mass to be 2.1 Earth-masses. The results, especially when compared with other planets’ properties, suggest that this planet may be rocky and likely to be “tidally locked” with one side of the planet always facing the star.

If there were liquid water on the surface of TOI-700d, the astronomers argue, there would also be water-bearing clouds in the atmosphere, and the team uses climate system models to estimate its possible properties and what more sensitive measurements might find. They conclude, however, that pending space missions, including JWST, will probably lack the sensitivity to detect atmospheric features by a factor of ten or more. Their detailed climate studies will nevertheless help astronomers constrain the kinds of telescopes and instruments that will be needed to investigate this exciting new neighbor.

Reference(s):

“The First Habitable-zone Earth-sized Planet from TESS. I. Validation of the TOI-700 System,” Emily A. Gilbert et al., The Astronomical Journal 160, 116, 2020.

“The First Habitable-zone Earth-sized Planet from TESS. II. Spitzer Confirms TOI-700 d,” Joseph E. Rodriguez et al., The Astronomical Journal 160, 117, 2020.

“The First Habitable-zone Earth-sized Planet from TESS. III. Climate States and Characterization Prospects for TOI-700 d,” Gabrielle Suissa, Eric T. Wolf, Ravi kumar Kopparapu, Geronimo L. Villanueva, Thomas Fauchez, Avi M. Mandell, Giada Arney, Emily A. Gilbert, Joshua E. Schlieder, Thomas Barclay, Elisa V. Quintana, Eric Lopez, Joseph E. Rodriguez , and Andrew Vanderburg, The Astronomical Journal 160, 118, 2020.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “The Monster in the Middle of the Milky Way Is…Spinning Slowly?”

From Harvard-Smithsonian Center for Astrophysics

October 20, 2020

Amy Oliver
Public Affairs
Center for Astrophysics | Harvard & Smithsonian
Fred Lawrence Whipple Observatory
520-879-4406
amy.oliver@cfa.harvard.edu

This wide-field view of the center of our Milky Way galaxy shows, in visible light, the vast array of stars contained within this small space. The stars closest to the center of the galaxy, known as S-stars, are orbiting SgrA*, a massive black hole. The orbits of these stars are helping scientists to better understand the black hole and the nature of our galaxy.

This view was created from photographs in red and blue light and forming part of the Digitized Sky Survey 2. The field of view is approximately 3.5 degrees x 3.6 degrees. Credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin and S. Guisard.

SgrA* NASA/Chandra supermassive black hole at the center of the Milky Way, X-ray image of the center of our galaxy, where the supermassive black hole Sagittarius A* resides. Image via X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI.

SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory.

The monstrous black hole at the center of the Milky Way galaxy—now of Nobel Prize fame—is proving yet again to be stranger than fiction. New research from scientists at the Center for Astrophysics | Harvard & Smithsonian (CfA), and the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) at Northwestern University has revealed that the supermassive black hole at the center of the Milky Way galaxy is not spinning much, providing more evidence that it is unlikely to have a jet. The paper is published in The Astrophysical Journal Letters.

Supermassive black holes like SgrA*—the monstrous black hole at the center of the Milky Way galaxy—are characterized by just two numbers: mass and spin, but have a critical influence on the formation and evolution of galaxies. According to Dr. Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard and CfA astronomer, and co-author on the research, “black holes release a huge amount of energy that removes gas from galaxies and therefore shapes their star formation history.”

While scientists know that the mass of central black holes has a critical influence on their host galaxy, measuring the impact of their spin isn’t easy. As Loeb puts it, “the effect of black hole spin on the orbits of nearby stars is subtle and difficult to measure directly.”

To get a better understanding of how Sgr A* has impacted formation and evolution of the Milky Way, Loeb and Dr. Giacomo Fragione, of CIERA, studied instead the stellar orbits and spatial distribution of S-stars—the closest stars orbiting SgrA* and traveling at a speed of up to a few percent of the speed of light—to constrain, or place limits on the spin of the black hole. “We concluded that the supermassive black hole in the center of our galaxy is spinning slowly,” said Fragione. “This can have major implications for the detectability of activity in the center of our galaxy and the future observations of the Event Horizon Telescope.”

Star S0-2 Andrea Ghez Keck/UCLA Galactic Center Group at SGR A*, the supermassive black hole at the center of the Milky Way.

The S-stars appear to be organized into two preferred planes. Loeb and Fragione showed that if Sgr A* had a significant spin, the preferred orbital planes of the stars at birth would become misaligned by the present time. “For our study we used the recently discovered S-stars to show that the spin of the black hole SgrA* must be smaller than than 10-percent of its maximal value, corresponding to a black hole spinning at the speed of light,” said Loeb. “Otherwise, the common orbital planes of these stars would not stay aligned during their lifetime, as seen today.”

The results of the research also point to another important detail about Sgr A*: it is unlikely to have a jet. “Jets are thought to be powered by spinning black holes, which act as giant flywheels,” said Loeb, with Fragione adding that, “Indeed there is no evidence of jet activity in SgrA*. Upcoming analysis of data from the Event Horizon Telescope will shed more light on this issue.”

The find was published just days before the announcement of the 2020 Nobel Prize in Physics, which was awarded in part to scientists Reinhard Genzel and Andrea Ghez for their ground-breaking research which demonstrated that SgrA* is a black hole. “Genzel and Ghez monitored the motion of stars around it,” said Loeb. “They measured its mass but not its spin. We have derived the first tight limit on SgrA*’s spin,” adding that the find wouldn’t be possible without Genzel and Ghez’s original Nobel Prize-winning work.

This work was supported in part by a CIERA Fellowship at Northwestern University, and Harvard’s Black Hole Initiative, which is funded by grants from the John Templeton Foundation and the Gordon and Betty Moore Foundation.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Planet Formation in Stellar Infancy”

From Harvard-Smithsonian Center for Astrophysics

October 16, 2020

The disk around the young star IRS63 (it is only about five hundred thousand years old) as imaged by ALMA at millimeter wavelengths. Its two rings and two gaps are labeled with R and G respectively; the scale length in astronomical units is shown. This is the youngest stellar disk ever imaged and its non-distinct edges suggest that at this early stage planets (but perhaps something else) have only just begun to shape the disk into the sharply defined rings and gaps seen in older systems. Credit: Segura-Cox et al. 2020; ALMA.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres.

As the slightly spinning material in a pre-stellar condensation collapses to form a star, angular momentum conservation shapes it into a circumstellar disk. Planets form from the gas and dust in these disks, whose structure and evolution are thus keys to unraveling the planet-building process. There are currently two favored scenarios, a core accretion model in which planets assemble through the aggregation of dust grains and a gravitational instability model in which clumps develop during the initial stages of the disk evolution and grow into planetesimals.

Astronomers have been able to image disks in over one hundred young stars so far and infer their presence in many more. Thirty-five of the imaged disks are only about one million years old and have recently begun to disperse the natal cloud of material from which they were born. Imaged at submillimeter wavelengths where the cool dust radiates efficiently, these disks reveal bright rings and empty gaps which are thought to be due to the presence of young planets that shepherd the dust into rings and clear out the gaps. These discoveries imply, however, that planet formation must have begun at even earlier stages — but no younger stars with disk have been discovered, until now.

CfA astronomer Ian Stephens was a member of a team that used the ALMA millimeter facility to image the object IRS63 whose disk had been identified by the Submillimeter Array but with insufficient resolution to see rings.

CfA Submillimeter Array Mauna Kea, Hawaii, USA, Altitude 4,080 m (13,390 ft).

The infrared emission from this system indicates it is younger than about five hundred thousand years. The star is relatively nearby, only about five hundred light-years distant; ALMA images can resolve structures as small as five astronomical units (one AU is the average Earth-Sun distance), and they reveal two rings and two gaps, the first detection of such protoplanetary disks in such a young star. Notably, the rings and gaps appear to be much less mature than those around older stars in the sense that the rings are much less well-defined and the gaps are not yet cleared of dust. The inner ring is situated about twenty-seven AU from the star, and the outer ring is about fifty-one AU away.

The scientists caution that concentric circumstellar annular structures do not by themselves require the presence of planets. A variety of other physical processes might produce similar structures including disk winds or the asymmetric accretion of material from an outer envelope. However even if planets have not yet formed, or if the dust grains have not yet coalesced into large masses, these dust rings around such an early stage star could serve as ideal zones for future planetesimal development. The new paper, appearing in the latest Nature, is an important step in constraining the earliest stages of planet formation.

Science paper:
Four Annular Structures in a Protostellar Disk Less Than 500,000 Years Old
Nature

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 Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.