Categories
ScienceDaily

Can life survive a star’s death? Webb telescope can reveal the answer

When stars like our sun die, all that remains is an exposed core — a white dwarf. A planet orbiting a white dwarf presents a promising opportunity to determine if life can survive the death of its star, according to Cornell University researchers.

In a study published in the Astrophysical Journal Letters, they show how NASA’s upcoming James Webb Space Telescope could find signatures of life on Earth-like planets orbiting white dwarfs.

A planet orbiting a small star produces strong atmospheric signals when it passes in front, or “transits,” its host star. White dwarfs push this to the extreme: They are 100 times smaller than our sun, almost as small as Earth, affording astronomers a rare opportunity to characterize rocky planets.

“If rocky planets exist around white dwarfs, we could spot signs of life on them in the next few years,” said corresponding author Lisa Kaltenegger, associate professor of astronomy in the College of Arts and Sciences and director of the Carl Sagan Institute.

Co-lead author Ryan MacDonald, a research associate at the institute, said the James Webb Space Telescope, scheduled to launch in October 2021, is uniquely placed to find signatures of life on rocky exoplanets.

“When observing Earth-like planets orbiting white dwarfs, the James Webb Space Telescope can detect water and carbon dioxide within a matter of hours,” MacDonald said. “Two days of observing time with this powerful telescope would allow the discovery of biosignature gases, such as ozone and methane.”

The discovery of the first transiting giant planet orbiting a white dwarf (WD 1856+534b), announced in a separate paper — led by co-author Andrew Vanderburg, assistant professor at the University of Wisconsin, Madison — proves the existence of planets around white dwarfs. Kaltenegger is a co-author on this paper, as well.

This planet is a gas giant and therefore not able to sustain life. But its existence suggests that smaller rocky planets, which could sustain life, could also exist in the habitable zones of white dwarfs.

“We know now that giant planets can exist around white dwarfs, and evidence stretches back over 100 years showing rocky material polluting light from white dwarfs. There are certainly small rocks in white dwarf systems,” MacDonald said. “It’s a logical leap to imagine a rocky planet like the Earth orbiting a white dwarf.”

The researchers combined state-of-the-art analysis techniques routinely used to detect gases in giant exoplanet atmospheres with the Hubble Space Telescope with model atmospheres of white dwarf planets from previous Cornell research.

NASA’s Transiting Exoplanet Survey Satellite is now looking for such rocky planets around white dwarfs. If and when one of these worlds is found, Kaltenegger and her team have developed the models and tools to identify signs of life in the planet’s atmosphere. The Webb telescope could soon begin this search.

The implications of finding signatures of life on a planet orbiting a white dwarf are profound, Kaltenegger said. Most stars, including our sun, will one day end up as white dwarfs.

“What if the death of the star is not the end for life?” she said. “Could life go on, even once our sun has died? Signs of life on planets orbiting white dwarfs would not only show the incredible tenacity of life, but perhaps also a glimpse into our future.”

Story Source:

Materials provided by Cornell University. Original written by Kate Blackwood. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

How stars form in the smallest galaxies

The question of how small, dwarf galaxies have sustained the formation of new stars over the course of the Universe has long confounded the world’s astronomers. An international research team led by Lund University in Sweden has found that dormant small galaxies can slowly accumulate gas over many billions of years. When this gas suddenly collapses under its own weight, new stars are able to arise.

There are around 2,000 billion galaxies in our Universe and, while our own Milky-Way encompasses between 200 and 400 billion stars, small dwarf galaxies contain only a thousand times less. How stars are formed in these tiny galaxies has long been shrouded in mystery.

However, in a new study published in the research journal Monthly Notices of the Royal Astronomical Society, a research team led from Lund University has established that dwarf galaxies are capable of lying dormant for several billion years before starting to form stars again.

“It is estimated that these dwarf galaxies stopped forming stars around 12 billion years ago. Our study shows that this can be a temporary hiatus,” says Martin Rey, an astrophysicist at Lund University and the leader of the study.

Through high-resolution computer simulations, the researchers demonstrate that star formation in dwarf galaxies ceased as a result of the heating and ionisation from the strong light of newborn stars. Explosions of so-called white dwarfs — small faint stars made of the core that remains when normal-sized stars die -further contribute in preventing the star formation process in dwarf galaxies.

“Our simulations show that dwarf galaxies are able to accumulate fuel in the form of gas, which eventually condenses and gives birth to stars. This explains the observed star formation in existing faint dwarf galaxies that has long puzzled astronomers,” states Martin Rey.

The computer simulations used by the researchers in the study are amongst the most expensive that can be carried out within physics. Each simulation takes as long as two months and requires the equivalent of 40 laptop computers operating around the clock. The work is continuing with the development of methods to better explain the processes behind star formation in our Universe’s smallest galaxies.

“By deepening our understanding of this subject, we gain new insights into the modelling of astrophysical processes such as star explosions, as well as the heating and cooling of cosmic gas. In addition, further work is underway to predict how many such star-forming dwarfs exist in our Universe, and could be discovered by astronomical telescopes” concludes Martin Rey.

Story Source:

Materials provided by Lund University. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

‘Black dwarf supernova’: Physicist calculates when the last supernova ever will happen

The end of the universe as we know it will not come with a bang. Most stars will very, very slowly fizzle as their temperatures fade to zero.

“It will be a bit of a sad, lonely, cold place,” said theoretical physicist Matt Caplan, who added no one will be around to witness this long farewell happening in the far far future. Most believe all will be dark as the universe comes to an end. “It’s known as ‘heat death,’ where the universe will be mostly black holes and burned-out stars,” said Caplan, who imagined a slightly different picture when he calculated how some of these dead stars might change over the eons.

Punctuating the darkness could be silent fireworks — explosions of the remnants of stars that were never supposed to explode. New theoretical work by Caplan, an assistant professor of physics at Illinois State University, finds that many white dwarfs may explode in supernova in the distant far future, long after everything else in the universe has died and gone quiet.

In the universe now, the dramatic death of massive stars in supernova explosions comes when internal nuclear reactions produce iron in the core. Iron cannot be burnt by stars — it accumulates like a poison, triggering the star’s collapse creating a supernova. But smaller stars tend to die with a bit more dignity, shrinking and becoming white dwarfs at the end of their lives.

“Stars less than about 10 times the mass of the sun do not have the gravity or density to produce iron in their cores the way massive stars do, so they can’t explode in a supernova right now,” said Caplan. “As white dwarfs cool down over the next few trillion years, they’ll grow dimmer, eventually freeze solid, and become ‘black dwarf’ stars that no longer shine.” Like white dwarfs today, they’ll be made mostly of light elements like carbon and oxygen and will be the size of the Earth but contain about as much mass as the sun, their insides squeezed to densities millions of times greater than anything on Earth.

But just because they’re cold doesn’t mean nuclear reactions stop. “Stars shine because of thermonuclear fusion — they’re hot enough to smash small nuclei together to make larger nuclei, which releases energy. White dwarfs are ash, they’re burnt out, but fusion reactions can still happen because of quantum tunneling, only much slower, Caplan said. “Fusion happens, even at zero temperature, it just takes a really long time.” He noted this is the key for turning black dwarfs into iron and triggering a supernova.

Caplan’s new work, accepted for publication by Monthly Notices of the Royal Astronomical Society, calculates how long these nuclear reactions take to produce iron, and how much iron black dwarfs of different sizes need to explode. He calls his theoretical explosions “black dwarf supernova” and calculates that the first one will occur in about 10 to the 1100th years. “In years, it’s like saying the word ‘trillion’ almost a hundred times. If you wrote it out, it would take up most of a page. It’s mindbogglingly far in the future.”

Of course, not all black dwarfs will explode. “Only the most massive black dwarfs, about 1.2 to 1.4 times the mass of the sun, will blow.” Still, that means as many as 1 percent of all stars that exist today, about a billion trillion stars, can expect to die this way. As for the rest, they’ll remain black dwarfs. “Even with very slow nuclear reactions, our sun still doesn’t have enough mass to ever explode in a supernova, even in the far far future. You could turn the whole sun to iron and it still wouldn’t pop.”

Caplan calculates that the most massive black dwarfs will explode first, followed by progressively less massive stars, until there are no more left to go off after about 1032000 years. At that point, the universe may truly be dead and silent. “It’s hard to imagine anything coming after that, black dwarf supernova might be the last interesting thing to happen in the universe. They may be the last supernova ever.” By the time the first black dwarfs explode, the universe will already be unrecognizable. “Galaxies will have dispersed, black holes will have evaporated, and the expansion of the universe will have pulled all remaining objects so far apart that none will ever see any of the others explode.It won’t even be physically possible for light to travel that far.”

Even though he’ll never see one, Caplan remains unbothered. “I became a physicist for one reason. I wanted to think about the big questions- why is the universe here, and how will it end?” When asked what big question comes next, Caplan says, “Maybe we’ll try simulating some black dwarf supernova. If we can’t see them in the sky then at least we can see them on a computer.”

Go to Source
Author:

Categories
ScienceDaily

Unequal neutron-star mergers create unique ‘bang’ in simulations

When two neutron stars slam together, the result is sometimes a black hole that swallows all but the gravitational evidence of the collision. However, in a series of simulations, an international team of researchers including a Penn State scientist determined that these typically quiet — at least in terms of radiation we can detect on Earth — collisions can sometimes be far noisier.

“When two incredibly dense collapsed neutron stars combine to form a black hole, strong gravitational waves emerge from the impact,” said David Radice, assistant professor of physics and of astronomy and astrophysics at Penn State and a member of the research team. “We can now pick up these waves using detectors like LIGO in the United States and Virgo in Italy. A black hole typically swallows any other radiation that could have come out of the merger that we would be able to detect on Earth, but through our simulations, we found that this may not always be the case.”

The research team found that when the masses of the two colliding neutron stars are different enough, the larger companion tears the smaller apart. This causes a slower merger that allows an electromagnetic “bang” to escape. Astronomers should be able to detect this electromagnetic signal, and the simulations provide signatures of these noisy collisions that astronomers could look for from Earth.

The research team, which includes members of the international collaboration CoRe (Computational Relativity), describe their findings in a paper appearing online in the Monthly Notices of the Royal Astronomical Society.

“Recently, LIGO announced the discovery of a merger event in which the two stars have possibly very different masses,” said Radice. “The main consequence in this scenario is that we expect this very characteristic electromagnetic counterpart to the gravititational wave signal.”

After reporting the first detection of a neutron-star merger in 2017, in 2019, the LIGO team reported the second, which they named GW190425. The result of the 2017 collision was about what astronomers expected, with a total mass of about 2.7 times the mass of our sun and each of the two neutron stars about equal in mass. But GW190425 was much heavier, with a combined mass of around 3.5 solar masses and the ratio of the two participants more unequal — possibly as high as 2 to 1.

“While a 2 to 1 difference in mass may not seem like a large difference, only a small range of masses is possible for neutron stars,” said Radice.

Neutron stars can exist only in a narrow range of masses between about 1.2 and 3 times the mass of our sun. Lighter stellar remnants don’t collapse to form neutron stars and instead form white dwarfs, while heavier objects collapse directly to form black holes. When the difference between the merging stars gets as large as in GW190425, scientists suspected that the merger could be messier — and louder in electromagnetic radiation. Astronomers had detected no such signal from GW190425’s location, but coverage of that area of the sky by conventional telescopes that day wasn’t good enough to rule it out.

To understand the phenomenon of unequal neutron stars colliding, and to predict signatures of such collisions that astronomers could look for, the research team ran a series of simulations using Pittsburgh Supercomputing Center’s Bridges platform and the San Diego Supercomputer Center’s Comet platform — both in the National Science Foundation’s XSEDE network of supercomputing centers and computers — and other supercomputers.

The researchers found that as the two simulated neutron stars spiraled in toward each other, the gravity of the larger star tore its partner apart. That meant that the smaller neutron star didn’t hit its mbrore massive companion all at once. The initial dump of the smaller star’s matter turned the larger into a black hole. But the rest of its matter was too far away for the black hole to capture immediately. Instead, the slower rain of matter into the black hole created a flash of electromagnetic radiation.

The research team hopes that the simulated signature they found can help astronomers using a combination of gravitational-wave detectors and conventional telescopes to detect the paired signals that would herald the breakup of a smaller neutron star merging with a larger.

The simulations required an unusual combination of computing speed, massive amounts of memory, and flexibility in moving data between memory and computation. The team used about 500 computing cores, running for weeks at a time, over about 20 separate instances. The many physical quantities that had to be accounted for in each calculation required about 100 times as much memory as a typical astrophysical simulation.

“There is a lot of uncertainty surrounding the properties of neutron stars,” said Radice. “In order to understand them, we have to simulate many possible models to see which ones are compatible with astronomical observations. A single simulation of one model would not tell us much; we need to perform a large number of fairly computationally intensive simulations. We need a combination of high capacity and high capability that only machines like Bridges can offer. This work would not have been possible without access to such national supercomputing resources.”

Story Source:

Materials provided by Penn State. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

Surprising number of exoplanets could host life

Our solar system has one habitable planet — Earth. A new study shows other stars could have as many as seven Earth-like planets in the absence of a gas giant like Jupiter.

This is the conclusion of a study led by UC Riverside astrobiologist Stephen Kane published this week in the Astronomical Journal.

The search for life in outer space is typically focused on what scientists call the “habitable zone,” which is the area around a star in which an orbiting planet could have liquid water oceans — a condition for life as we know it.

Kane had been studying a nearby solar system called Trappist-1, which has three Earth-like planets in its habitable zone.

“This made me wonder about the maximum number of habitable planets it’s possible for a star to have, and why our star only has one,” Kane said. “It didn’t seem fair!”

His team created a model system in which they simulated planets of various sizes orbiting their stars. An algorithm accounted for gravitational forces and helped test how the planets interacted with each other over millions of years.

They found it is possible for some stars to support as many as seven, and that a star like our sun could potentially support six planets with liquid water.

“More than seven, and the planets become too close to each other and destabilize each other’s orbits,” Kane said.

Why then does our solar system only have one habitable planet if it is capable of supporting six? It helps if the planets’ movement is circular rather than oval or irregular, minimizing any close contact and maintain stable orbits.

Kane also suspects Jupiter, which has a mass two-and-a-half times that of all the other planets in the solar system combined, limited our system’s habitability.

“It has a big effect on the habitability of our solar system because it’s massive and disturbs other orbits,” Kane said.

Only a handful of stars are known to have multiple planets in their habitable zones. Moving forward, Kane plans to search for additional stars surrounded entirely by smaller planets. These stars will be prime targets for direct imaging with NASA telescopes like the one at Jet Propulsion Laboratory’s Habitable Exoplanet Observatory.

Kane’s study identified one such star, Beta CVn, which is relatively close by at 27 light years away. Because it doesn’t have a Jupiter-like planet, it will be included as one of the stars checked for multiple habitable zone planets.

Future studies will also involve the creation of new models that examine the atmospheric chemistry of habitable zone planets in other star systems.

Projects like these offer more than new avenues in the search for life in outer space. They also offer scientists insight into forces that might change life on our own planet one day.

“Although we know Earth has been habitable for most of its history, many questions remain regarding how these favorable conditions evolved with time, and the specific drivers behind those changes,” Kane said. “By measuring the properties of exoplanets whose evolutionary pathways may be similar to our own, we gain a preview into the past and future of this planet — and what we must do to main its habitability.”

Story Source:

Materials provided by University of California – Riverside. Original written by Jules Bernstein. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

Strange dismembered star cluster found at Galaxy’s edge

An international team of astronomers has discovered the remnant of an ancient collection of stars that was torn apart by our own galaxy, the Milky Way, more than two billion years ago.

The extraordinary discovery of this shredded ‘globular cluster’ is surprising, as the stars in this galactic archaeological find have much lower quantities of heavier elements than in other such clusters. The evidence strongly suggests the original structure was the last of its kind, a globular cluster whose birth and life were different to those remaining today.

Our Galaxy is home to about 150 globular clusters, each a ball of a million or so stars that orbit in the Galaxy’s tenuous stellar halo. These globular clusters are old and have witnessed the growth of the Milky Way over billions of years.

The study, published in Nature, was led by University of Sydney PhD student, Zhen Wan, and his supervisor, Professor Geraint Lewis, as part of the S5 international collaboration.

Using the Anglo-Australian Telescope in outback New South Wales, this collaboration measured the speeds of a stream of stars in the Phoenix constellation, revealing them to be remnants of a globular cluster that was pulled apart by the gravity of the Milky Way about two billion years ago.

Mr Wan said: “Once we knew which stars belonged to the stream, we measured their abundance of elements heavier than hydrogen and helium; something astronomers refer to as metallicity. We were really surprised to find that the Phoenix Stream has a very low metallicity, making it distinctly different to all of the other globular clusters in the Galaxy.

“Even though the cluster was destroyed billions of years ago, we can still tell it formed in the early Universe from the composition of its stars.”

HEAVY METALS

After the Big Bang, only hydrogen and helium existed in any substantial amount in the Universe. These elements formed the first generation of stars many billions of years ago. It is within these and later stellar generations that heavier elements were formed, such as the calcium, oxygen and phosphorus that in part make up your bones.

Observations of other globular clusters have found that their stars are enriched with heavier elements forged in earlier generations of stars. Current formation theories suggest that this dependence on previous stars means that no globular cluster should be found unenriched and that there is a minimum metallicity ‘floor’ below which no cluster can form.

But the metallicity of the Phoenix Stream progenitor sits well below this minimum, posing a significant problem for our ideas of globular cluster origins.

“This stream comes from a cluster that, by our understanding, shouldn’t have existed,” said co-author Associate Professor Daniel Zucker from Macquarie University.

S5 team leader, Dr Ting Li from Carnegie Observatories, said: “One possible explanation is that the Phoenix Stream represents the last of its kind, the remnant of a population of globular clusters that was born in radically different environments to those we see today.”

While potentially numerous in the past, this population of globular clusters was steadily depleted by the gravitational forces of the Galaxy, which tore them to pieces, absorbing their stars into the main body of the galactic system. This means that the stream is a relatively temporary phenomenon, which will dissipate in time.

“We found the remains of this cluster before it faded forever into the Galaxy’s halo,” Mr Wan said.

As yet, there is no clear explanation for the origins of the Phoenix Stream progenitor cluster and where it sits in the evolution of galaxies remains unclear.

Professor Lewis said: “There is plenty of theoretical work left to do. There are now many new questions for us to explore about how galaxies and globular clusters form, which is incredibly exciting.”

Is the Phoenix Stream unique? “In astronomy, when we find a new kind of object, it suggests that there are more of them out there,” said co-author Dr Jeffrey Simpson from the University of New South Wales. While globular clusters like the progenitor of the Phoenix Stream may no longer exist, their remnants may live on as faint streams.”

Dr Li said: “The next question to ask is whether there are more ancient remnants out there, the leftovers of a population that no longer exists. Finding more such streams will give us a new view of what was going on in the early Universe.”

“This is a regime we have hardly explored. It’s a very exciting time,” she said.

Go to Source
Author:

Categories
ScienceDaily

White dwarfs reveal new insights into the origin of carbon in the universe

A new analysis of white dwarf stars supports their role as a key source of carbon, an element crucial to all life, in the Milky Way and other galaxies.

Approximately 90 percent of all stars end their lives as white dwarfs, very dense stellar remnants that gradually cool and dim over billions of years. With their final few breaths before they collapse, however, these stars leave an important legacy, spreading their ashes into the surrounding space through stellar winds enriched with chemical elements, including carbon, newly synthesized in the star’s deep interior during the last stages before its death.

Every carbon atom in the universe was created by stars, through the fusion of three helium nuclei. But astrophysicists still debate which types of stars are the primary source of the carbon in our own galaxy, the Milky Way. Some studies favor low-mass stars that blew off their envelopes in stellar winds and became white dwarfs, while others favor massive stars that eventually exploded as supernovae.

In the new study, published July 6 in Nature Astronomy, an international team of astronomers discovered and analyzed white dwarfs in open star clusters in the Milky Way, and their findings help shed light on the origin of the carbon in our galaxy. Open star clusters are groups of up to a few thousand stars, formed from the same giant molecular cloud and roughly the same age, and held together by mutual gravitational attraction. The study was based on astronomical observations conducted in 2018 at the W. M. Keck Observatory in Hawaii and led by coauthor Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at UC Santa Cruz.

“From the analysis of the observed Keck spectra, it was possible to measure the masses of the white dwarfs. Using the theory of stellar evolution, we were able to trace back to the progenitor stars and derive their masses at birth,” Ramirez-Ruiz explained.

The relationship between the initial masses of stars and their final masses as white dwarfs is known as the initial-final mass relation, a fundamental diagnostic in astrophysics that integrates information from the entire life cycles of stars, linking birth to death. In general, the more massive the star at birth, the more massive the white dwarf left at its death, and this trend has been supported on both observational and theoretical grounds.

But analysis of the newly discovered white dwarfs in old open clusters gave a surprising result: the masses of these white dwarfs were notably larger than expected, putting a “kink” in the initial-final mass relation for stars with initial masses in a certain range.

“Our study interprets this kink in the initial-final mass relationship as the signature of the synthesis of carbon made by low-mass stars in the Milky Way,” said lead author Paola Marigo at the University of Padua in Italy.

In the last phases of their lives, stars twice as massive as our Sun produced new carbon atoms in their hot interiors, transported them to the surface, and finally spread them into the interstellar medium through gentle stellar winds. The team’s detailed stellar models indicate that the stripping of the carbon-rich outer mantle occurred slowly enough to allow the central cores of these stars, the future white dwarfs, to grow appreciably in mass.

Analyzing the initial-final mass relation around the kink, the researchers concluded that stars bigger than 2 solar masses also contributed to the galactic enrichment of carbon, while stars of less than 1.5 solar masses did not. In other words, 1.5 solar masses represents the minimum mass for a star to spread carbon-enriched ashes upon its death.

These findings place stringent constraints on how and when carbon, the element essential to life on Earth, was produced by the stars of our galaxy, eventually ending up trapped in the raw material from which the Sun and its planetary system were formed 4.6 billion years ago.

“Now we know that the carbon came from stars with a birth mass of not less than roughly 1.5 solar masses,” said Marigo.

Coauthor Pier-Emmanuel Tremblay at University of Warwick said, “One of most exciting aspects of this research is that it impacts the age of known white dwarfs, which are essential cosmic probes to understand the formation history of the Milky Way. The initial-to-final mass relation is also what sets the lower mass limit for supernovae, the gigantic explosions seen at large distances and that are really important to understand the nature of the universe.”

By combining the theories of cosmology and stellar evolution, the researchers concluded that bright carbon-rich stars close to their death, quite similar to the progenitors of the white dwarfs analyzed in this study, are presently contributing to a vast amount of the light emitted by very distant galaxies. This light, carrying the signature of newly produced carbon, is routinely collected by large telescopes to probe the evolution of cosmic structures. A reliable interpretation of this light depends on understanding the synthesis of carbon in stars.

Go to Source
Author:

Categories
ScienceDaily

Orb hidden in distant dust is ‘infant’ planet

Astronomers study stars and planets much younger than the Sun to learn about past events that shaped the Solar System and Earth. Most of these stars are far enough away to make observations challenging, even with the largest telescopes. But now this is changing.

University of Hawai’i at Manoa astronomers are part of an international team that recently discovered an infant planet around a nearby young star. The discovery was reported Wednesday in the international journal Nature.

The planet is about the size of Neptune, but, unlike Neptune, it is much closer to its star, taking only eight and a half days to complete one orbit. It is named “AU Mic b” after its host star, AU Microscopii, or “AU Mic” for short. The planet was discovered using the NASA TESS planet-finding satellite, as it periodically passed in front of AU Mic, blocking a small fraction of its light. The signal was confirmed by observations with another NASA satellite, the Spitzer Space Telescope, and with the NASA Infrared Telescope Facility (IRTF) on Maunakea. The observations on Hawai’i Island used a new instrument called iSHELL that can make very precise measurements of the motion of a star like AU Mic. These measurements revealed a slight wobble of the star, as it moves in response to the gravitational pull of the planet. It confirmed that AU Mic b was a planet and not a companion star, which would cause a much larger motion.

Discovery on Maunakea sets foundation

AU Mic and its planet are about 25 million years young, and in their infancy, astronomically speaking. AU Mic is also the second closest young star to Earth. It is so young that dust and debris left over from its formation still orbit around it. The debris collides and breaks into smaller dust particles, which orbit the star in a thin disk. This disk was detected in 2003 with the UH 88-inch telescope on Maunakea. The newly-discovered planet orbits within a cleared-out region inside the disk.

“This is an exciting discovery, especially as the planet is in one of the most well-known young star systems, and the second-closest to Earth. In addition to the debris disk, there is always the possibility of additional planets around this star. AU Mic could be the gift that keeps on giving,” said Michael Bottom, an Assistant Astronomer at the UH Institute for Astronomy.

“Planets, like people, change as they mature. For planets this means that their orbits can move and the compositions of their atmospheres can change. Some planets form hot and cool down, and unlike people, they would become smaller over time. But we need observations to test these ideas and planets like AU Mic b are an exceptional opportunity,” said Astronomer Eric Gaidos, a professor in the Department of Earth Sciences at UH M?noa.

Clues to the origin of Earth-like planets

AU Mic is not only much younger than the Sun, it is considerably smaller, dimmer and redder. It is a “red dwarf,” the most numerous type of star in the galaxy. The TESS satellite is also discovering Earth-sized and possibly habitable planets around older red dwarfs, and what astronomers learn from AU Mic and AU Mic b can be applied to understand the history of those planets.

“AU Mic b, and any kindred planets that are discovered in the future, will be intensely studied to understand how planets form and evolve. Fortuitously, this star and its planet are on our cosmic doorstep. We do not have to venture very far to see the show,” Gaidos explained. He is a co-author on another five forthcoming scientific publications that have used other telescopes, including several on Maunakea, to learn more about AU Mic and its planet.

AU Mic appears low in the summer skies of Hawai’i but you’ll need binoculars to see it. Despite its proximity, the fact that it is a dim red star means it is too faint to be seen with the unaided eye.

Story Source:

Materials provided by University of Hawaii at Manoa. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

X-ray scattering enables closer scrutiny of the interior of planets and stars

Recreating extreme conditions in the lab, like those in the interior of planets and stars, is very complex and can only be achieved for fractions of a second. An international research team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now presented a new, very precise method of evaluating the behavior of mixtures of different elements under high pressure with the help of X-ray scattering. The results hone previous measurements and reinforce the premise that the matter in planets like Neptune and Uranus can alter dramatically: the hot hydrocarbon mixture in the interior of the ice giants can produce a kind of diamond rain, as the researchers report in Nature Communications.

Neither solid, nor fluid, neither gaseous, nor a plasma: the matter inside planets and stars can take on a particular intermediate state, at a temperature of thousands of degrees, and compressed a thousand times more than our Earth’s atmosphere — experts call it warm dense matter. There is a lot we still don’t know about it. Lab experiments are set to change all that but are technically highly complex because this exotic state does not occur naturally on Earth. Which all means that both the crafting and study of artificial warm dense matter is a challenge for investigators and theoreticians alike. “But in the last resort, we have to understand the processes in warm dense matter if we want to model planets,” explains Dr. Dominik Kraus, lead author of the study and the mastermind behind the measuring method. “We now have a very promising new approach based on X-ray scattering. Our experiments are delivering important model parameters where, before, we only had massive uncertainty. This will become ever more relevant the more exoplanets we discover.”

Diamond showers — a planetary energy source

At SLAC National Accelerator Laboratory at Stanford University, the researchers studied the structure of the matter in mixtures that are typical for planets, in the case of ice giants, hydrocarbon, employing intense laser light. Standard plastic film served as a substitute for planetary hydrocarbon. An optical high-energy laser converts the plastic into warm dense matter: short, strong laser pulses generate shock waves in the film and compress the plastic to the extreme. “We produce about 1.5 million bars, that is equivalent to the pressure exerted by the weight of some 250 African elephants on the surface of a thumbnail,” says Kraus, illustrating the dimensions. What happens is that the laser shock waves also heat up the matter to approximately 5,000 degrees. To evaluate the effect, researchers shoot an extremely powerful X-ray laser at the sample. Depending on how the light is scattered as it passes through the sample, they can draw inferences about the structure of the matter.

The researchers observed that in a state of warm dense matter, what was formerly plastic produces diamonds. The high pressure can split the hydrocarbon into carbon and hydrogen. The carbon atoms that are released compact into diamond structures. In the case of planets like Neptune and Uranus this means that the formation of diamonds in their interior can trigger an additional energy source. The diamonds are heavier than the matter surrounding them and slowly sink to the core of the planet in a kind of diamond rain. In the process, they rub against their surroundings and generate heat — an important factor for planet models.

X-ray scattering enhances measuring precision

In an earlier experiment, Kraus and his team were the first to prove the possible formation of diamonds in planets using X-ray diffraction in an experimental setting. But the diffraction patterns of X-ray light can only reveal crystalline structures. Using additional detectors, the researchers now also analyzed how the light was scattered by the electrons in the matter. They compared the various scattering components with one another as well as with theoretical simulations. This process enables precise scrutiny of the entire structure of matter. “In the case of the ice giants we now know that the carbon almost exclusively forms diamonds when it separates and does not take on a fluid transitional form,” explains Kraus.

The method is not only more sensitive than X-ray diffraction, it can also be used more extensively because it makes fewer technical demands on the light source for the analysis. The international research team is now planning to apply it to hydrogen mixtures similar to those that occur in gaseous planets and to compressed pure hydrogen as found in the interior of small stars. These experiments, which are planned to be conducted, among others, at the Helmholtz International Beamline for Extreme Fields (HIBEF) at the European XFEL, could help researchers to understand the many planets we already know about outside our solar system to ascertain whether life might even be possible on any of them.

Fusion experiments could benefit practically from the new measuring method, as well. Fusion research also tries to recreate on Earth processes that occur under great pressure in stars. During inertial confinement fusion, deuterium and tritium fuels are heated to extremes and compressed — warm dense matter is an intermediate state. With the help of X-ray scattering, this process could be monitored precisely.

Story Source:

Materials provided by Helmholtz-Zentrum Dresden-Rossendorf. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

Mystery astronomical object in ‘mass gap’: Neutron star? Black hole?

When the most massive stars die, they collapse under their own gravity and leave behind black holes; when stars that are a bit less massive die, they explode in supernovas and leave behind dense, dead remnants of stars called neutron stars. For decades, astronomers have been puzzled by a gap that lies between neutron stars and black holes: the heaviest known neutron star is no more than 2.5 times the mass of our sun, or 2.5 solar masses, and the lightest known black hole is about 5 solar masses. The question remained: does anything lie in this so-called mass gap?

Now, in a new study from the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo detector in Europe, scientists have announced the discovery of an object of 2.6 solar masses, placing it firmly in the mass gap. The object was found on August 14, 2019, as it merged with a black hole of 23 solar masses, generating a splash of gravitational waves detected back on Earth by LIGO and Virgo. A paper about the detection is being published today, June 23, in The Astrophysical Journal Letters.

“We’ve been waiting decades to solve this mystery” says co-author Vicky Kalogera, a professor at Northwestern University. “We don’t know if this object is the heaviest known neutron star, or the lightest known black hole, but either way it breaks a record.”

“This is going to change how scientists talk about neutron stars and black holes,” says co-author Patrick Brady, a professor at the University of Wisconsin, Milwaukee, and the LIGO Scientific Collaboration spokesperson. “The mass gap may in fact not exist at all but may have been due to limitations in observational capabilities. Time and more observations will tell.”

The cosmic merger described in the study, an event dubbed GW190814, resulted in a final black hole about 25 times the mass of the sun (some of the merged mass was converted to a blast of energy in the form of gravitational waves). The newly formed black hole lies about 800 million light-years away from Earth.

Before the two objects merged, their masses differed by a factor of 9, making this the most extreme mass ratio known for a gravitational-wave event. Another recently reported LIGO-Virgo event, called GW190412, occurred between two black holes with a mass ratio of about 4:1.

“It’s a challenge for current theoretical models to form merging pairs of compact objects with such a large mass ratio in which the low-mass partner resides in the mass gap. This discovery implies these events occur much more often than we predicted, making this a really intriguing low-mass object,” explains Kalogera. “The mystery object may be a neutron star merging with a black hole, an exciting possibility expected theoretically but not yet confirmed observationally. However, at 2.6 times the mass of our sun, it exceeds modern predictions for the maximum mass of neutron stars, and may instead be the lightest black hole ever detected.”

When the LIGO and Virgo scientists spotted this merger, they immediately sent out an alert to the astronomical community. Dozens of ground- and space-based telescopes followed up in search of light waves generated in the event, but none picked up any signals. So far, such light counterparts to gravitational-wave signals have been seen only once, in an event called GW170817. That event, discovered by the LIGO-Virgo network in August of 2017, involved a fiery collision between two neutron stars that was subsequently witnessed by dozens of telescopes on Earth and in space. Neutron star collisions are messy affairs with matter flung outward in all directions and are thus expected to shine with light. Conversely, black hole mergers, in most circumstances, are thought not to produce light.

According to the LIGO and Virgo scientists, the August 2019 event was not seen by light-based telescopes for a few possible reasons. First, this event was six times farther away than the merger observed in 2017, making it harder to pick up any light signals. Secondly, if the collision involved two black holes, it likely would have not shone with any light. Thirdly, if the object was in fact a neutron star, its 9-fold more massive black-hole partner might have swallowed it whole; a neutron star consumed whole by a black hole would not give off any light.

“I think of Pac-Man eating a little dot,” says Kalogera. “When the masses are highly asymmetric, the smaller neutron star can be eaten in one bite.”

How will researchers ever know if the mystery object was a neutron star or a black hole? Future observations with LIGO, Virgo, and possibly other telescopes may catch similar events that would help reveal whether additional objects exist in the mass gap.

“This is the first glimpse of what could be a whole new population of compact binary objects,” says Charlie Hoy, a member of the LIGO Scientific Collaboration and a graduate student at Cardiff University. “What is really exciting is that this is just the start. As the detectors get more and more sensitive, we will observe even more of these signals, and we will be able to pinpoint the populations of neutron stars and black holes in the universe.”

“The mass gap has been an interesting puzzle for decades, and now we’ve detected an object that fits just inside it,” says Pedro Marronetti, program director for gravitational physics at the National Science Foundation (NSF). “That cannot be explained without defying our understanding of extremely dense matter or what we know about the evolution of stars. This observation is yet another example of the transformative potential of the field of gravitational-wave astronomy, which brings novel insights with every new detection.”

Go to Source
Author: