Showing posts with label Astronomy. Show all posts
Showing posts with label Astronomy. Show all posts

Monday, September 20, 2021

Physicists probe light smashups to guide future research

 
The Compact Muon Solenoid experiment at the
European Organization for Nuclear Research’s
Large Hadron Collider.
Photo courtesy of CERN
Hot on the heels of proving an 87-year-old prediction that matter can be generated directly from light, Rice University physicists and their colleagues have detailed how that process may impact future studies of primordial plasma and physics beyond the Standard Model.

“We are essentially looking at collisions of light,” said Wei Li, an associate professor of physics and astronomy at Rice and co-author of the study published in Physical Review Letters.

Rice physicists teamed with colleagues at Europe’s Large Hadron Collider to study matter-generating collisions of light. Researchers showed the departure angle of debris from the smashups is subtly distorted by quantum interference patterns in the light prior to impact. Illustration by 123rf.com

“We know from Einstein that energy can be converted into mass,” said Li, a particle physicist who collaborates with hundreds of colleagues on experiments at high-energy particle accelerators like the European Organization for Nuclear Research’s Large Hadron Collider (LHC) and Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC).

Accelerators like RHIC and LHC routinely turn energy into matter by accelerating pieces of atoms near the speed of light and smashing them into one another. The 2012 discovery of the Higgs particle at the LHC is a notable example. At the time, the Higgs was the final unobserved particle in the Standard Model, a theory that describes the fundamental forces and building blocks of atoms.

Impressive as it is, physicists know the Standard Model explains only about 4% of the matter and energy in the universe. Li said this week’s study, which was lead-authored by Rice postdoctoral researcher Shuai Yang, has implications for the search for physics beyond the Standard Model.

Thursday, September 9, 2021

ESO captures best images yet of peculiar “dog-bone” asteroid

 
These eleven images are of the asteroid Kleopatra, viewed at different angles as it rotates. The images were taken at different times between 2017 and 2019 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s VLT.   Kleopatra orbits the Sun in the Asteroid Belt between Mars and Jupiter. Astronomers have called it a “dog-bone asteroid” ever since radar observations around 20 years ago revealed it has two lobes connected by a thick “neck”. 
Credit / Source: ESO/Vernazza, Marchis et al./MISTRAL algorithm (ONERA/CNRS)

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), a team of astronomers have obtained the sharpest and most detailed images yet of the asteroid Kleopatra. The observations have allowed the team to constrain the 3D shape and mass of this peculiar asteroid, which resembles a dog bone, to a higher accuracy than ever before. Their research provides clues as to how this asteroid and the two moons that orbit it formed.

“Kleopatra is truly a unique body in our Solar System,” says Franck Marchis, an astronomer at the SETI Institute in Mountain View, USA and at the Laboratoire d'Astrophysique de Marseille, France, who led a study on the asteroid — which has moons and an unusual shape — published today in Astronomy & Astrophysics. “Science makes a lot of progress thanks to the study of weird outliers. I think Kleopatra is one of those and understanding this complex, multiple asteroid system can help us learn more about our Solar System.”

Kleopatra orbits the Sun in the Asteroid Belt between Mars and Jupiter. Astronomers have called it a “dog-bone asteroid” ever since radar observations around 20 years ago revealed it has two lobes connected by a thick “neck”. In 2008, Marchis and his colleagues discovered that Kleopatra is orbited by two moons, named AlexHelios and CleoSelene, after the Egyptian queen’s children.

To find out more about Kleopatra, Marchis and his team used snapshots of the asteroid taken at different times between 2017 and 2019 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s VLT. As the asteroid was rotating, they were able to view it from different angles and to create the most accurate 3D models of its shape to date. They constrained the asteroid’s dog-bone shape and its volume, finding one of the lobes to be larger than the other, and determined the length of the asteroid to be about 270 kilometers or about half the length of the English Channel.

This image provides a size comparison of the asteroid Kleopatra with northern Italy.   The top half of the image shows a computer model of Kleopatra, a “dog-bone” shaped asteroid which orbits the Sun in the Asteroid Belt between Mars and Jupiter. End to end, Kleopatra is 270 kilometers long.   The bottom half of the image gives an aerial view of northern Italy, with the footprint Kleopatra would have if it were hovering above it.   
Credit / Sou: ESO/M. Kornmesser/Marchis et al.
In a second study, also published in Astronomy & Astrophysics and led by Miroslav Brož of Charles University in Prague, Czech Republic, the team reported how they used the SPHERE observations to find the correct orbits of Kleopatra’s two moons. Previous studies had estimated the orbits, but the new observations with ESO’s VLT showed that the moons were not where the older data predicted them to be.

“This had to be resolved,” says Brož. “Because if the moons’ orbits were wrong, everything was wrong, including the mass of Kleopatra.” Thanks to the new observations and sophisticated modelling, the team managed to precisely describe how Kleopatra’s gravity influences the moons’ movements and to determine the complex orbits of AlexHelios and CleoSelene. This allowed them to calculate the asteroid’s mass, finding it to be 35% lower than previous estimates.

Combining the new estimates for volume and mass, astronomers were able to calculate a new value for the density of the asteroid, which, at less than half the density of iron, turned out to be lower than previously thought. The low density of Kleopatra, which is believed to have a metallic composition, suggests that it has a porous structure and could be little more than a “pile of rubble”. This means it likely formed when material reaccumulated following a giant impact.

Kleopatra’s rubble-pile structure and the way it rotates also give indications as to how its two moons could have formed. The asteroid rotates almost at a critical speed, the speed above which it would start to fall apart, and even small impacts may lift pebbles off its surface. Marchis and his team believe that those pebbles could subsequently have formed AlexHelios and CleoSelene, meaning that Kleopatra has truly birthed its own moons.

The new images of Kleopatra and the insights they provide are only possible thanks to one of the advanced adaptive optics systems in use on ESO’s VLT, which is located in the Atacama Desert in Chile. Adaptive optics help to correct for distortions caused by the Earth’s atmosphere which cause objects to appear blurred — the same effect that causes stars viewed from Earth to twinkle. Thanks to such corrections, SPHERE was able to image Kleopatra — located 200 million kilometers away from Earth at its closest — even though its apparent size on the sky is equivalent to that of a golf ball about 40 kilometers away.

ESO’s upcoming Extremely Large Telescope (ELT), with its advanced adaptive optics systems, will be ideal for imaging distant asteroids such as Kleopatra. “I can’t wait to point the ELT at Kleopatra, to see if there are more moons and refine their orbits to detect small changes,” adds Marchis.

Source/Credit: ESO

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Released
09-09-21 12:00UTC

Monday, September 6, 2021

Hubble Discovers Hydrogen-Burning White Dwarfs Enjoying Slow Ageing

To investigate the physics underpinning white dwarf evolution, astronomers compared cooling white dwarfs in two massive collections of stars: the globular clusters M3 and M13. These two clusters share many physical properties such as age and metallicity but the populations of stars which will eventually give rise to white dwarfs are different. This makes M3 and M13 together a perfect natural laboratory in which to test how different populations of white dwarfs cool.
Image credit: ESA/Hubble & NASA, G. Piotto et al.

Could dying stars hold the secret to looking younger? New evidence from the NASA/ESA Hubble Space Telescope suggests that white dwarfs could continue to burn hydrogen in the final stages of their lives, causing them to appear more youthful than they actually are. This discovery could have consequences for how astronomers measure the ages of star clusters.

The prevalent view of white dwarfs as inert, slowly cooling stars has been challenged by observations from the NASA/ESA Hubble Space Telescope. An international group of astronomers have discovered the first evidence that white dwarfs can slow down their rate of ageing by burning hydrogen on their surface.

“We have found the first observational evidence that white dwarfs can still undergo stable thermonuclear activity,” explained Jianxing Chen of the Alma Mater Studiorum Università di Bologna and the Italian National Institute for Astrophysics, who led this research. “This was quite a surprise, as it is at odds with what is commonly believed.”

White dwarfs are the slowly cooling stars which have cast off their outer layers during the last stages of their lives. They are common objects in the cosmos; roughly 98% of all the stars in the Universe will ultimately end up as white dwarfs, including our own Sun [1]. Studying these cooling stages helps astronomers understand not only white dwarfs, but also their earlier stages as well.

To investigate the physics underpinning white dwarf evolution, astronomers compared cooling white dwarfs in two massive collections of stars: the globular clusters M3 and M13 [2]. These two clusters share many physical properties such as age and metallicity [3] but the populations of stars which will eventually give rise to white dwarfs are different. In particular, the overall colour of stars at an evolutionary stage known as the Horizontal Branch are bluer in M13, indicating a population of hotter stars. This makes M3 and M13 together a perfect natural laboratory in which to test how different populations of white dwarfs cool.

“The superb quality of our Hubble observations provided us with a full view of the stellar populations of the two globular clusters,” continued Chen. “This allowed us to really contrast how stars evolve in M3 and M13.”

Using Hubble’s Wide Field Camera 3 the team observed M3 and M13 at near-ultraviolet wavelengths, allowing them to compare more than 700 white dwarfs in the two clusters. They found that M3 contains standard white dwarfs which are simply cooling stellar cores. M13, on the other hand, contains two populations of white dwarfs: standard white dwarfs and those which have managed to hold on to an outer envelope of hydrogen, allowing them to burn for longer and hence cool more slowly.

Comparing their results with computer simulations of stellar evolution in M13, the researchers were able to show that roughly 70% of the white dwarfs in M13 are burning hydrogen on their surfaces, slowing down the rate at which they are cooling. 

This discovery could have consequences for how astronomers measure the ages of stars in the Milky Way. The evolution of white dwarfs has previously been modelled as a predictable cooling process. This relatively straightforward relationship between age and temperature has led astronomers to use the white dwarf cooling rate as a natural clock to determine the ages of star clusters, particularly globular and open clusters. However, white dwarfs burning hydrogen could cause these age estimates to be inaccurate by as much as 1 billion years.

“Our discovery challenges the definition of white dwarfs as we consider a new perspective on the way in which stars get old,” added Francesco Ferraro of the Alma Mater Studiorum Università di Bologna and the Italian National Institute for Astrophysics, who coordinated the study. “We are now investigating other clusters similar to M13 to further constrain the conditions which drive stars to maintain the thin hydrogen envelope which allows them to age slowly”. 

Notes

[1] The Sun is only 4.6 billion years through its roughly 10-billion-year lifetime. Once it exhausts hydrogen in its core, the Sun will swell into a red giant, engulfing the inner planets and searing the Earth’s surface. It will then throw off its outer layers, and the exposed core of the Sun will be left as a slowly cooling white dwarf. This stellar ember will be incredibly dense, packing a large fraction of the mass of the Sun into a roughly Earth-sized sphere.

[2] M3 contains roughly half a million stars and lies in the constellation Canes Venatici. M13 — occasionally known as the Great Globular Cluster in Hercules — contains slightly fewer stars, only several hundred thousand. White dwarfs are often used to estimate the ages of globular clusters, and so a significant amount of Hubble time has been dedicated to exploring white dwarfs in old and densely populated globular clusters. Hubble directly observed white dwarfs in globular star clusters for the first time in 2006.

[3] Astronomers use the word “metallicity” to describe the proportion of a star which is composed of elements other than hydrogen and helium. The vast majority of matter in the Universe is either hydrogen or helium — to take the Sun as an example, 74.9% of its mass is hydrogen, 23.8% is helium, and the remaining 1.3% is a mixture of all the other elements, which astronomers refer to as “metals”

Source/Credit: ESA/Hubble

sn090621_01

Thursday, September 2, 2021

A Black Hole Triggers a Premature Supernova

 

Dillon Dong, with a 27-meter radio dish at
Caltech's Owens Valley Radio Observatory in the background.
In 2017, a particularly luminous and unusual source of radio waves was discovered in data taken by the Very Large Array (VLA) Sky Survey, a project that scans the night sky in radio wavelengths. Now, led by Caltech graduate student Dillon Dong (MS '18), a team of astronomers has established that the bright radio flare was caused by a black hole or neutron star crashing into its companion star in a never-before-seen process.

"Massive stars usually explode as supernovae when they run out of nuclear fuel," says Gregg Hallinan, professor of astronomy at Caltech. "But in this case, an invading black hole or neutron star has prematurely triggered its companion star to explode." This is the first time a merger-triggered supernova has ever been confirmed.

Bright Flares in the Night Sky

Hallinan and his team look for so-called radio transients—short-lived sources of radio waves that flare
brightly and burn out quickly like a match lit in a dark room. Radio transients are an excellent way to identify unusual astronomical events, such as massive stars that explode and blast out energetic jets or the mergers of neutron stars.

As Dong sifted through the VLA's massive dataset, he singled out an extremely luminous source of radio waves from the VLA survey called VT 1210+4956. This source is tied for the brightest radio transient ever associated with a supernova.

Dong determined that the bright radio energy was originally a star surrounded by a thick and dense shell of gas. This gas shell had been cast off the star a few hundred years before the present day. VT 1210+4956, the radio transient, occurred when the star finally exploded in a supernova and the material ejected from the explosion interacted with the gas shell. Yet, the gas shell itself, and the timescale on which it was cast off from the star, were unusual, so Dong suspected that there might be more to the story of this explosion.

Two Unusual Events

Following Dong's discovery, Caltech graduate student Anna Ho (PhD '20) suggested that this radio transient be compared with a different catalog of brief bright events in the X-ray spectrum. Some of these X-ray events were so short-lived that they were only present in the sky for a few seconds of Earth time. By examining this other catalog, Dong discovered a source of X-rays that originated from the same spot in the sky as VT 1210+4956. Through careful analysis, Dong established that the X-rays and the radio waves were likely coming from the same event.

Gregg Hallinan

"The X-ray transient was an unusual event—it signaled that a relativistic jet was launched at the time of the explosion," says Dong. "And the luminous radio glow indicated that the material from that explosion later crashed into a massive torus of dense gas that had been ejected from the star centuries earlier. These two events have never been associated with each other, and on their own they're very rare."

A Mystery Solved

So, what happened? After careful modeling, the team determined the most likely explanation—an event that involved some of the same cosmic players that are known to generate gravitational waves.

They speculated that a leftover compact remnant of a star that had previously exploded—that is, a black hole or a neutron star—had been closely orbiting around a star. Over time, the black hole had begun siphoning away the atmosphere of its companion star and ejecting it into space, forming the torus of gas. This process dragged the two objects ever closer until the black hole plunged into the star, causing the star to collapse and explode as a supernova.

The X-rays were produced by a jet launched from the core of the star at the moment of its collapse. The radio waves, by contrast, were produced years later as the exploding star reached the torus of gas that had been ejected by the inspiraling compact object.

Astronomers know that a massive star and a companion compact object can form what is called a stable orbit, in which the two bodies gradually spiral closer and closer over an extremely long period of time. This process forms a binary system that is stable for millions to billions of years but that will eventually collide and emit the kind of gravitational waves that were discovered by LIGO in 2015 and 2017.

However, in the case of VT 1210+4956, the two objects instead collided immediately and catastrophically, producing the blasts of X-rays and radio waves observed. Although collisions such as this have been predicted theoretically, VT 1210+4956 provides the first concrete evidence that it happens.

Serendipitous Surveying

The VLA Sky Survey produces enormous amounts of data about radio signals from the night sky, but sifting through that data to discover a bright and interesting event such as VT 1210+4956 is like finding a needle in a haystack. Finding this particular needle, Dong says, was, in a way, serendipitous.

"We had ideas of what we might find in the VLA survey, but we were open to the possibility of finding things we didn't expect," explains Dong. "We created the conditions to discover something interesting by conducting loosely constrained, open-minded searches of large data sets and then taking into account all of the contextual clues we could assemble about the objects that we found. During this process you find yourself pulled in different directions by different explanations, and you simply let nature tell you what's out there."

The paper is titled "A transient radio source consistent with a merger-triggered core collapse supernova." Dillon Dong is the first author. In addition to Hallinan and Ho, additional co-authors are Ehud Nakar, Andrew Hughes, Kenta Hotokezaka, Steve Myers (PhD '90), Kishalay De (MS '18, PHD '21), Kunal Mooley (PhD '15), Vikram Ravi, Assaf Horesh, Mansi Kasliwal (MS '07, PhD '11), and Shri Kulkarni. Funding was provided by the National Science Foundation, the United States–Israel Binational Science Foundation, the I-Core Program of the Planning and Budgeting Committee and the Israel Science Foundation, Canada's Natural Sciences and Engineering Research Council, the Miller Institute for Basic Research in Science at the UC Berkeley, the Japan Society for the Promotion of Science Early-Career Scientists Program, the National Radio Astronomy Observatory, and the Heising-Simons Foundation.

A paper about the findings will appear in the journal Science on September 3.

Source/Credit: California Institute of Technology / Lori Dajose

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What's Up September 2021

 


Source/Credit: NASA/JPL

Wednesday, August 25, 2021

Astrophysical data to unravel the universe’s mysteries

 The University of Washington and Carnegie Mellon University have announced an expansive,

Rubin Observatory summit facility in Cerro Pachón, Chile.Rubin Observatory/NSF/AURA

multiyear collaboration to create new software platforms to analyze large astronomical datasets generated by the upcoming Legacy Survey of Space and Time, or LSST, which will be carried out by the Vera C. Rubin Observatory in northern Chile. The open-source platforms are part of the new LSST Interdisciplinary Network for Collaboration and Computing — known as LINCC — and will fundamentally change how scientists use modern computational methods to make sense of big data.

Through the LSST, the Rubin Observatory, a joint initiative of the National Science Foundation and the Department of Energy, will collect and process more than 20 terabytes of data each night — and up to 10 petabytes each year for 10 years — and will build detailed composite images of the southern sky. Over its expected decade of observations, astrophysicists estimate the Department of Energy’s LSST Camera will detect and capture images of an estimated 30 billion stars, galaxies, stellar clusters and asteroids. Each point in the sky will be visited around 1,000 times over the survey’s 10 years, providing researchers with valuable time series data.

Scientists plan to use this data to address fundamental questions about our universe, such as the formation of our solar system, the course of near-Earth asteroids, the birth and death of stars, the nature of dark matter and dark energy, the universe’s murky early years and its ultimate fate, among other things.

“Tools that utilize the power of cloud computing will allow any researcher to search and analyze data at the scale of the LSST, not just speeding up the rate at which we make discoveries but changing the scientific questions that we can ask,” said Andrew Connolly, a UW professor of astronomy, director of the eScience Institute and former director of the Data Intensive Research in Astrophysics and Cosmology Institute — commonly known as the DiRAC Institute.

The Rubin Observatory will produce an unprecedented data set through the LSST. To take advantage of this opportunity, the LSST Corporation created the LSST Interdisciplinary Network for Collaboration and Computing, whose launch was announced Aug. 9 at the Rubin Observatory Project & Community Workshop. One of LINCC’s primary goals is to create new and improved analysis infrastructure that can accommodate the data’s scale and complexity that will result in meaningful and useful pipelines of discovery for LSST data.

“Many of the LSST’s science objectives share common traits and computational challenges. If we develop our algorithms and analysis frameworks with forethought, we can use them to enable many of the survey’s core science objectives,” said Rachel Mandelbaum, professor of physics and member of the McWilliams Center for Cosmology at Carnegie Mellon.

Connolly and Mandelbaum will co-lead the project, which will consist of programmers and scientists based at the UW and Carnegie Mellon, who will create platforms using professional software engineering practices and tools. Specifically, they will create a “cloud-first” system that also supports high-performance computing systems in partnership with the Pittsburgh Supercomputing Center, a joint effort of Carnegie Mellon and the University of Pittsburgh, and the National Science Foundation’s NOIRLab. The LSST Corporation will run programs to engage the LSST Science Collaborations and broader science community in the design, testing and use of the new tools.

The complete focal plane of the LSST Camera is more than 2 feet wide and contains 189 individual sensors that will produce 3200-megapixel images.Jacqueline Orrell/SLAC National Accelerator Laboratory/NSF/DOE/Rubin Observatory/AURA

The LINCC analysis platforms are supported by Schmidt Futures, a philanthropic initiative founded by Eric and Wendy Schmidt that “bets early on exceptional people making the world better.” This project is part of Schmidt Futures’ work in astrophysics, which aims to accelerate our knowledge about the universe by supporting the development of software and hardware platforms to facilitate research across the field of astronomy.

“Many years ago, the Schmidt family provided one of the first grants to advance the original design of the Vera C. Rubin Observatory. We believe this telescope is one of the most important and eagerly awaited instruments in astrophysics in this decade. By developing platforms to analyze the astronomical datasets captured by the LSST, Carnegie Mellon University and the University of Washington are transforming what is possible in the field of astronomy,” said Stuart Feldman, chief scientist at Schmidt Futures. "The software funded by this gift will magnify the scientific return on the public investment by the National Science Foundation and the Department of Energy to build and operate Rubin Observatory’s revolutionary telescope, camera and data systems,” said Adam Bolton, director of the Community Science and Data Center at NSF’s NOIRLab. The center will collaborate with LINCC scientists and engineers to make the LINCC framework accessible to the broader astronomical community.

Through this new project, new algorithms and processing pipelines developed at LINCC will be able to be used across fields within astrophysics and cosmology to sift through false signals, filter out noise in the data and flag potentially important objects for follow-up observations. The tools developed by LINCC will support a “census of our solar system” that will chart the courses of asteroids; help researchers to understand how the universe changes with time; and build a 3D view of the universe’s history.

“Our goal is to maximize the scientific output and societal impact of Rubin LSST, and these analysis tools will go a huge way toward doing just that,” said Jeno Sokoloski, director for science at the LSST Corporation. “They will be freely available to all researchers, students, teachers and members of the general public.”

Northwestern University and the University of Arizona, in addition to the UW and Carnegie Mellon, are hub sites for LINCC. The University of Pittsburgh will partner with the Carnegie Mellon hub.

UW, Carnegie Mellon to pioneer platforms that harness astrophysical data to unravel the universe’s mysteries

Source / Credit: University of Washington

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