Astronomers discover extremely luminous nova

First nova ever found in Small Magellanic Cloud is studied in multiple wavelengths.

What might be one of the most luminous stars ever detected is actually a nova or explosion that occurred in a binary system consisting of a white dwarf and Sun-like star in the Small Magellanic Cloud.

White dwarfs are stellar remnants of stars not massive enough to have died in supernova explosions.

The Small Magellanic Cloud is a satellite galaxy of the Milky Way located about 200,000 light years away.

Using NASA’s Swift satellite, scientists at the University of Leicester discovered the extremely bright nova, caused by the white dwarf’s sucking of material from the regular star until critical pressure was reached, causing the sudden brightness increase.

Led by researchers at the South African Astronomical Observatory, the scientists also observed the nova with ground-based telescopes in several countries, including South Africa, Australia, and South America.

Designated SMCN 2016-10a, the nova, one of the brightest observed in any galaxy, was discovered on October 14, 2016.

The term “nova” means new. Centuries ago, astronomers thought these suddenly bright objects to be new stars as opposed to what they really are–dying old ones.

White dwarfs emit both visible light and high-energy X-rays. By studying their emissions in various wavelengths, scientists can determine their temperatures and compositions.

This is the first time astronomers have spotted a nova in the Small Magellanic Cloud. Approximately 35 are seen in the Milky Way each year.

“Swift’s ability to respond rapidly, together with its daily-planned schedule, makes it ideal for the followup of transients, including novae,” said Swift team X-ray analysis leader Kim Page of the University of Leicester.

“It was able to observe the nova throughout its eruption, starting to collect very useful X-ray and UV data within a day of the outburst first being reported. The X-ray data were essential in showing that the mass of the white dwarf is close to the theoretical maximum; continued accretion might cause it eventually to be totally destroyed in a supernova explosion.”

Paul Kuin of the Mullard Space Science Laboratory at University College London, who organized the UV data, described the ability to observe the nova in multiple wavelengths as key to this being the most comprehensive nova study ever conducted.

Findings of the study have been published in Monthly Notices of the Royal Astronomical Society.

Astronomers find remnant of 600-year-old nova

Based on the Korean astronomers’ description of the phenomenon, scientists today believe the outburst occurred in a binary system that contained a dead, highly dense white dwarf star and a companion.

A three-decade search for the remnant of a nova recorded by Korean astronomers almost 600 years ago has finally succeeded in finding the location of the stellar remnant.

Michael Shara, astrophysics coordinator at New York’s American Museum of Natural History, said the hunt for Nova Scorpii AD 1437 took so long because Korean records did not assign numbers or names to nearby stars, resulting in his team inadvertently looking  in the wrong location.

Novae are nuclear explosions that occur at the end stages of massive stars’ lives. Unlike the more powerful supernovae, which completely destroy their precursor stars, standard novae leave the remains of their parent stars intact.

Fifteenth-century Korean astronomers recorded what they believed was a new star that appeared on March 11, 1437 near a known star in the tail of the constellation Scorpius. The bright “new” star was visible for two weeks before disappearing.

Based on the Korean astronomers’ description of the phenomenon, scientists today believe the outburst occurred in a binary system that contained a dead, highly dense white dwarf star and a companion.

Over time, white dwarfs funnel material out of their companion stars, eventually causing them to explode.

Known as cataclysmic variables, binary systems composed of a white dwarf and a regular star experience many novae over time and possibly smaller explosions known as dwarf novae.

By analyzing data collected by the South African Large Telescope and Las Campanas Observatory’s Swope and du Pont telescopes, along with reviewing digital images of photographic plates of the sky taken by Harvard University for more than 100 years, the research team located debris from the nova in the constellation Scorpius.

Calculations of neighboring stars’ motions over the last six centuries confirmed a binary system once resided in the location where the nova was originally seen.

Evidence of dwarf novae in this location on photographic plates from the 1930s and 1940s suggests the binary system is producing both classical and dwarf novae.

The researchers, who published their findings in the journal Nature, hope to image the nova to find out what it looks like now as well as locate several additional novae recorded in history to confirm that classical and dwarf novae have common origins.

ALMA photographs debris ring around young star Formalhaut

Disk’s chemical composition is strangely similar to that of comets in our solar system.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), a team of scientists has captured the first ever complete image of a ring of icy dust surrounding the young star Formalhaut.

The complete millimeter-wavelength of the ring reveals it to be a well-defined structure of dust and gas with a composition surprisingly similar to that of comets in our solar system.

Located approximately 25 light years away, Formalhaut has a planet initially discovered in 2008. It is one of only about 20 nearby star systems whose orbiting planets have been directly imaged.

The debris ring is approximately two billion kilometers wide at a distance of about 20 billion kilometers from the star.

At about 440 million years old, the system is just one-tenth as old as our solar system and may be experiencing its own version of the Late Heavy Bombardment that ours underwent about four billion years ago, a period characterized by asteroids and comets left over from the system’s formation repeatedly slamming into its planets.

Impacts of exocomets crashing into one another in the outer regions of the Formalhaut system likely created the debris ring, scientists believe.

A previous attempt to image the debris ring with ALMA in 2012, when the telescope was still in the process of being built, revealed just half of the disk but already hinted at chemical similarities with our solar system’s comets.

Now, “ALMA has given us this staggeringly clear image of a fully formed debris disk. We can finally see the well-defined shape of the disk, which may tell us a great deal about the underlying planetary system responsible for its highly distinctive appearance,” noted Meredith MacGregor of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, and lead author of two papers on the subject scheduled for publication in the Astrophysical Journal.

With the help of computer modeling, the researchers were able to pinpoint the exact location and shape of the disk. Based on its narrow shape, they believe it to be the product of the gravitational influence of planets orbiting the star.

Interestingly, the debris disk contains approximately the same high levels of both carbon monoxide and carbon dioxide found in our own solar system’s comets.

Impacts among numerous exocomets could be releasing these gases.

“This chemical kinship may indicate a similarity in comet formation conditions between the outer reaches of this planetary system and our own,” noted Luca Matra of the University of Cambridge in the UK and lead author of one of the two papers on the discovery.

 

 

Star, black hole interaction further proves Einstein’s theory

A new analysis on a distant black hole shows that Einstein’s theory of general relativity remains rock solid.

For the first time in history scientists have used a supermassive black hole’s gravitational field to confirm Einstein’s theory of general relativity, a new study in Astronomy & Astrophysics reports.

To do this, a team of international researchers analyzed the black hole at the center of the Milky Way — known as Sagittarius A — and a star in its orbit known as S2.

Using a combination of technology, mathematics, and observations, they studied the pair and observed S2 move close to the black hole. During that event, the fiery body acted exactly as predicted by the theory of relativity. 

“This is the second time that we have observed the close passage of S2 around the black hole in our galactic center,” said study co-author Reinhard Genzel, a researcher at the Max Planck Institute for Extraterrestrial Physics, according to Science Alert. “But this time, because of much improved instrumentation, we were able to observe the star with unprecedented resolution.”

Three S-stars orbit Sagittarius A, and S2 gets extremely close to the hole every now and then. In the recent study, it moved within just 17 light-hours of the formation.

That is significant because, according to Einstein’s theory, the event should have stretched S2’s light into long wavelengths through a process known as gravitational redshifting.

While it is not easy to observe S2, high-tech telescopes analyzed the star and revealed its light did behave in that way.

The finding falls in line with other recent studies that set out — and failed — to disprove the popular theory.

However, such trials are important because if the theory ever does fail it would drastically alter the way scientists view and understand both the universe and the field of physics. 

“What we hope is at some point we will see something in the galactic centre that we can’t explain with Einstein’s theory – that would be really, really exciting,” said study co-author Odele Straub, a researcher at the Paris Observatory in France, according to BBC News. “Because then we could go back to the drawing board and come up with something better.”

Scientists continue to explore mystery of Sun’s hot corona

Since the discovery of the hot corona, scientists have conducted many studies into its behavior.

Scientists are continuing their study of the Sun’s corona—the outermost of its atmosphere—to solve the mystery behind its high temperatures. Against all logic, it gets much hotter as it extends from the star’s hot surface.

“I think of the coronal heating problem as an umbrella that covers a couple of related confusing problems,” said Justin Kasper, a space scientist at the University of Michigan. “First, how does the corona get that hot that quickly? But the second part of the problem is that it doesn’t just start, it keeps going. And not only does heating continue, but different elements are heated at different rates.”

Since the discovery of the hot corona, scientists have conducted many studies into its behavior, including some that harness powerful instruments and models. Yet even the most comprehensive models and observations only somewhat explain coronal heating. Not only that, but some theories contradict one another.

“All of our work over the years has culminated to this point: We realized we can never fully solve the coronal heating problem until we send a probe to make measurements in the corona itself,” said Nour Raouafi, Parker Solar Probe deputy project scientist.

But by examining the heating from close-up, scientists are hoping to soon put the mystery to rest.

“We’re going close to the heating, and there are times Parker Solar Probe will co-rotate, or orbit the Sun at the same speed the Sun itself rotates,” said Eric Christian, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That’s an important part of the science. By hovering over the same spot, we’ll see the evolution of heating.”

X-ray data potentially reveals first evidence of a star devouring a planet

Researchers might have discovered the first evidence of a star, RW Aur A, devouring a planet.

A team of physicists might have just discovered the first-ever evidence of a star devouring a planet. The evidence would explain its most recent dimming event: the crash of two young planetary bodies that created debris that fell into the star, RW Aur A.

“Computer simulations have long predicted that planets can fall into a young star, but we have never before observed that,” said Hans Moritz Guenther, a research scientist from MIT who led the study. “If our interpretation of the data is correct, this would be the first time that we directly observe a young star devouring a planet or planets.”

The team believes the star’s previous dimming events could have been caused by similar collisions, of either remnants of past collisions that crashed into each other or the collision of two planetary bodies.

“It’s speculation, but if you have one collision of two pieces, it’s likely that afterward they may be on some rogue orbits, which increases the probability that they will hit something else again,” Guenther said.

“There are many processes that happen in young stars, but these two scenarios could possibly make something that looks like what we observed,” he said.

Regardless, Guenther hopes to continue making observations of the star.

“Much effort currently goes into learning about exoplanets and how they form, so it is obviously very important to see how young planets could be destroyed in interactions with their host stars and other young planets, and what factors determine if they survive,” he said.

Amateur astronomer discovers exocomets in Kepler data

Exocomets are smallest objects ever found orbiting a star other than the Sun.

An amateur astronomer who reviewed data collected by NASA’s Kepler exoplanet hunting telescope through the citizen science Planet Hunters program discovered unusual dips in a star’s light that scientists at MIT and other universities determined to be caused by exocomets.

The comets orbit a faint star approximately 800 light years from Earth.

This marks the first time that the transit method, which measures the dimming of a star’s light as a planet passes in front of it, discovered extremely small objects.

In contrast to the smallest exoplanets yet discovered, approximately one-third the size of the Earth, exocomets are tiny, making them very difficult to find.

Thomas Jacobs of Bellevue, Washington, an amateur astronomer and co-author of a paper on the discovery published in the Monthly Notices of the Royal Astronomical Society, began studying four years of exoplanet data collected by the initial Kepler mission, which included more than 200,000 stars and graphs showing the intensity of the light they emitted.

Planet Hunters engages volunteers to find patterns in Kepler data that computer algorithms missed, which could indicate the presence of exoplanets.

On March 18 of this year, he came upon three unusual light patterns, individual transits across the star KIC 3542116. Unlike planet transits, which occur at regular intervals, single transits indicate an object that passes in front of the star just once.

He then reported his findings to Saul Rappaport, a professor emeritus at MIT’s Kavli Institute for Astrophysics and Space Research, and Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics.

“We sat on this for a month because we didn’t know what it was–planet transits don’t look like this,” Rappaport said. “Then it occurred to me that, ‘Hey, these look like something we’ve seen before.'”

Unlike the light curves of transiting planets, those Jacobs found were asymmetrical and resembled those of planets that disintegrate after coming too close to their star, leaving behind long debris trails that block very small amounts of the star’s light.

“The only thing that fits the bill, and has a small enough mass to get destroyed, is a comet,” Rappaport emphasized.

Three more comet transits around the same star were subsequently found by the researchers.

From the data, scientists estimate the comets were about the size of Halley’s Comet in our solar system and traveled about 100,000 miles per hour before coming too close to the star and being vaporized.

Their gas and dust tails blocked approximately one percent of the star’s light as they transited.

“It’s amazing that something several orders of magnitude smaller than the Earth can be detected just by the fact that it’s emitting a lot of debris,” Rappaport noted.

Jacobs credits his finding to patience and perseverance. “For me, it is a form of treasure hunting, knowing that there is an interesting event waiting to be discovered. It is all about exploration and being on the hunt where few have traveled before.”

 

Debris disks of comets are coming together to form exoplanets

Planets are forming from multiple sites instead of growing from just one site.

Debris disks composed of comets surrounding stars in at least three stellar systems are coming together to form large exoplanets, planetary scientist Carey Lisse of the Johns Hopkins University Applied Physics Laboratory (JHUAPL) reported at the American Astronomical Society’s Division for Planetary Sciences meeting in Utah.

The narrow, dense rings were spotted in several star systems with NASA’s Spitzer Space Telescope and the Infrared Telescope Facility in Hawaii.

Located between 75 and 200 astronomical units (or AU, with one AU equal to the average Earth-Sun distance, or 93 million miles) from their stars, the bright debris rings have a variety of compositions. Some are rich in ice, such as Formalhaut and HD 32297, while others, such as HR 4796A, are rich in carbon but have little ice.

HR 4796A’s ring is unusually red, likely due to cometary remains. Because the ring is relatively close to the star, the comets likely burned away and left behind rocky organic materials.

No red dust is visible in the rings of Formalhaut or HD 32297. These rings are far enough from the star that comets within them remain intact, resulting in the rings being icy.

“The narrow confines of these rings is still a great puzzle–you don’t typically see this in such a young system,” Lisse said regarding the debris rings in these three systems.

“Usually, material is moving every which way before an exoplanetary system gets cleaned out and settles down so that planetary bodies rarely cross each other’s path, like in our present-day solar system.”

Based on the amount of light the ring systems reflect, the researchers were able to estimate their masses. Those estimates show the planets being formed are several times the size of the Earth.

Objects coming together within the debris rings appear to be “shepherding” other material through the rings.

“Comets crashing down onto these growing planet surfaces would kick up huge clouds of fast-moving, ejected ‘construction dust,’ which would spread over the system in huge clouds. The only apparent solution to these issues is that multiple mini-planets are coalescing in these rings, and these small bodies, with low kick-up velocities, are shepherding the rings into narrow structures–much in the same way many of the narrow rings of Saturn are focused and sharpened,” Lisse explained.

Millions of comet cores are believed to be coming together to form the cores of ice giant planets in Formalhaut and in HD 32297, much like the cores of Uranus and Neptune.

However, the planets in these systems will not have atmospheres, as the systems lack the primordial gas that creates those atmospheres.

In addition to ice giants, these systems also appear to be building super-Earths composed of rock, ice, and organic materials, Lisse said.

 

 

Scientists detect gravitational waves produced by colliding neutron stars

Ability to observe an event via both gravitational waves and light is a revolution for modern astronomy.

Scientists using the Laser Interferometer Gravitational Wave Observatory (LIGO) observatory have for the first time detected gravitational waves produced by a collision of two neutron stars in the galaxy NGC4993, located in the constellation Hydra.

Predicted in 1916 by Albert Einstein’s general theory of relativity, the ripples in the fabric of spacetime known as gravitational waves were first detected a century later by LIGO, caused by the merger of two black holes.

That detection led to three scientists winning the 2017 Nobel Prize in physics.

While gravitational waves have subsequently been detected several times since then, this is the first time they were observed coming from merging neutron stars rather than merging black holes.

Neutron stars are the stellar remnants of massive stars that died in supernova explosions. Extremely massive stars that die in supernova explosions leave behind black holes while less massive stars that die in these explosions produce neutron stars, which have cores somewhat less massive than black holes.

These extremely dense cores are capable of crushing protons and electrons to form neutrons.

Although neutron stars are small, with diameters of around 12 miles (19 km), they can be as dense as our Sun and have masses up to one billion tons.

Unlike black holes, which have gravitational pulls so strong that even light cannot escape them, neutron stars, in merging, emit light in multiple wavelengths.

This means their mergers can be observed both by the gravitational waves they produce and in various wavelengths of light.

Approximately 130 million years ago, two stars of between eight and 20 solar masses in the galaxy NGC4993 underwent supernova explosions, then orbited one another until they collided.

On August 17, LIGO and Virgo detected the gravitational waves produced by the collision, and a few minutes later, NASA’s Fermi space telescope observed a flash of gamma rays the explosion produced.

Once the gamma rays were detected, scientists knew the direction from which the gravitational waves came, and astronomers worldwide aimed telescopes at the phenomenon to collect additional data.

The double detection confirms that both light and gravitational waves travel at the same universal speed of light, another Einstein prediction.

“This event has the most precise sky localization of all detected gravitational waves so far,” said Virgo spokesman Jo van den Brand. “This record precision enabled astronomers to perform follow-up observations that led to a plethora of breathtaking results.”

More than 3,500 astronomers worldwide observed the event with over 70 telescopes.

Researchers studying the light spectra of material emitted during the merger found the fingerprints of heavy elements, including gold, platinum, and lead, confirming theories that the periodic table’s heaviest elements are forged in mergers of neutron stars.

 

Proxima b exoplanet might appear green

Auroras caused by powerful stellar flares could potentially be seen from Earth.

The planet orbiting Proxima Centauri, the star closest to our Sun, might appear greenish to observers if it has an Earth-like atmosphere.

That color would be the product of interaction between oxygen in its atmosphere and particles released by stellar activity.

Located 4.2 light years away, Proxima Centauri is an active star that undergoes more frequent stellar flares than our Sun.

It is also significantly smaller than the Sun, meaning its habitable zone is a region much closer to the star than the habitable zone of our solar system.

Approximately 20 times closer to Proxima Centauri than Earth is to our Sun, the planet, which has 1.3 Earth masses and is believed to be rocky, takes just 11.2 Earth days to complete a single orbit.

Exposed to more powerful and more frequent flares than Earth experiences, Proxima b could be subject to radiation levels that render it unable to support life.

The flares would also cause brilliant auroras on Proxima b if the planet has a magnetic field that can catch their charged particles and send them toward the planet’s poles.

If Proxima b’s atmosphere contains oxygen, these auroras, which would be 100 times more powerful than those on Earth, would appear green, according to a study led by Rodrigo Luger of the University of Washington and published in the journal Earth and Planetary Astrophysics.

These auroras would be so bright that observers on Earth using powerful telescopes would be capable of seeing them.

If scientists can successfully observe the auroras, they will be able to identify the components of the planet’s atmosphere.

One of the auroras’ effects would be that the planet would look like a “pale green dot” as opposed to the “pale blue dot,” a term Carl Sagan used to describe Earth from a great distance.

The various colors of Earth’s northern and southern auroras are produced by collisions between charged particles released in solar flares and various molecules in its atmosphere.