Stars – The Space Reporter

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.

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.

Merging neutron stars likely created a black hole

Though that alone made the merger worthy of study, it was also significant because it may have created the lowest mass black hole ever found.

The merging of two neutron stars may have created one of the most interesting black holes ever recorded, according to recent research published in the Astrophysical Journal Letters.

Last year, the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Europe-based Virgo detector detected a collision between two neutron stars that was so strong it generated gravitational waves.

Such an event had never been witnessed before. Though that alone made the merger worthy of study, it was also significant because it may have created the lowest mass black hole ever found.

In the study, scientists from Trinity University analyzed data from NASA’s Chandra X-ray Observatory taken before the technology noticed the gravitational waves in August 2017.

Matching that against data taken from LIGO, the team estimated the mass of the object created by the star merger has roughly 2.7 times the solar mass. That suggests it is either the lowest mass black hole or the highest mass neutron star ever recorded.

However, as a heavy neutron star would have produced both a strong magnetic field and X-rays — neither of which the team detected during their research — it is likely the collision led to a black hole.

“Astronomers have long suspected that neutron star mergers would form a black hole and produce bursts of radiation, but we lacked a strong case for it until now,” said study co-author Pawan Kumar, a researcher at the University of Texas, in a statement.

Though this study is compelling, it does not give definitive evidence that the merger created a neutron star. More research needs to be done on the event, including both X-ray and radio observations, before any hard conclusions can be reached.

“If the remnant is a rapidly rotating magnetized neutron star, the total energy in the external shock should rise by a factor ~102 (to ~1052 erg) after a few years; therefore, Chandra observations over the next year or two that do not show substantial brightening will rule out such a remnant,” the team wrote in their study, according to Tech Times.

Future humans could overcome expansion of the universe

Dyson spheres could be used to anchor stars within the Milky Way.

Existential threats to humanity range from urgent, to a distant possibility. One such remote threat is the accelerating expansion of the universe. While most wouldn’t consider this a real threat, particle physicist, Dan Hooper, at the Fermi National Accelerator Laboratory, points out why it is a threat we should consider.

He points out that things beyond the cosmic horizon—the maximum distance that light can travel to us within the age of the universe—are beyond our ability to study, or influence. Stars, galaxies, even civilizations are beyond the cosmic horizon, and beyond our ability to contact or see them. According to an article in MIT Technology Review discussing Hooper’s theory, the cosmic horizon is changing and this will affect our neighborhood in the universe, which astronomers call the Local Group. The Local Group (50 nearby galaxies bound to the Milky Way) will be humanity’s home for the foreseeable future. But these galaxies may not always be within our reach to possibly colonize, as the accelerating expansion of the universe sends galaxies over the horizon at a rate that’s increasing.

As Hooper explains, “over the next approximately 100 billion years, all stars residing beyond the Local Group will fall beyond the cosmic horizon and become not only unobservable, but entirely inaccessible.” This eventuality would interfere with humanity’s ability to exploit ever more stars for energy. However, Hooper believes there is a way to mitigate the effects of an expansion. He believes that an advanced civilization could build a Dyson sphere that emits waste radiation in a specific direction to accelerate the sphere—and the star it contains—in the opposite direction of the acceleration. Over time, this technology could be used to gather stars as a source of energy, keeping them inside the cosmic horizon. So, potential problem solved? Well, as the article acknowledges, first the assumption that the expansion of the universe is accelerating would have to be correct.

Jets of water vapor found streaming from newborn star

Various complex organic molecules also seen in star-forming region.

Astronomers who observed a turbulent star-forming region using the Atacama Large Millimeter/submillimeter Array’s (ALMA) highest frequency capabilities detected jets of water vapor streaming from a massive newborn star approximately 4,300 light years away.

ALMA uses an array of very precise antennas to study high-frequency radio light waves and was recently equipped with shortwave capabilities, enabling it to see a region in the electromagnetic spectrum at the boundary between infrared and radio wavelengths.

Located in the direction of the constellation Scorpius, the region observed, a section of the Cat’s Paw Nebula or NGC 63341, is an active stellar nursery. Previous ALMA observations of it at lower frequencies revealed it to be an active environment that harbors complex organic molecules.

On April 5, 2018, a team of scientists used ALMA to observe this region with the new, high-frequency technology. The Chilean observatory does this by assigning a series of “bands” designated one through 10, each of which studies a very small part of the spectrum. Band 10, the highest frequency, was used to look at the nebula’s star-forming region.

Two major discoveries were made from these observations–water vapor streaming away from a newborn star in jets and the fingerprints of a variety of molecules.

“High-frequency radio observations like these are normally not possible from the ground. They require the extreme precision and sensitivity of ALMA, along with some of the driest and most stable atmospheric conditions that can be found on Earth,” explained Brett McGuire of the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia.

ALMA detected the submillimeter wavelengths that are the fingerprints of light emitted by heavy water, a form of water in which some or all of the hydrogen molecules are replaced by the hydrogen isotope deuterium.

“Normally, we wouldn’t be able to directly see this particular signal at all from the ground. Earth’s atmosphere, even at remarkably arid places, still contains enough water vapor to completely overwhelm this signal from any cosmic source. During exceptionally pristine conditions in the high Atacama Desert, however, ALMA can in fact detect that signal. This is something no other telescope on Earth can achieve,” said Crystal Brogan, also of NRAO.

Most of the material in the protoplanetary disks surrounding baby stars falls onto them. However, a small amount of this material, including heavy water, gas, and other molecules, is instead directed away from these stars in the form of jets traveling in opposite outward directions.

A paper on the findings has been published in Astrophysical Journal Letters.

Astronomers report latest detection of radio bursts coming from space

The recent detection reflects lower frequencies than what astronomers have reported in the past.

Fast Radio Bursts (FRBs) are some of the most explosive events in the Universe. They can generate as much energy as 500 million Suns in milliseconds, and there could be as many as one happening every second, writes Fiona Macdonald for Science Alert. Now, astronomers report detection of another FRB hitting Earth from an unknown source. This particular radio burst falls within the lower end of the spectrum, within the 50 megahertz frequency range, nearly 200 MHz lower than any other signal scientists have detected before. FRBs are incredibly mysterious, astronomers don’t yet know what’s causing them.

Although one of the signals detected has sent out multiple FRBs from the same location—allowing scientists to pinpoint where in the Universes it’s coming from—they still aren’t certain what caused it. Most signals are only detected once, making it difficult for astronomers to determine the source. The recent FRB was detected on July 25, 2018 and reported in The Astronomer’s Telegram. It has been named FRB 180725A, and was caught by an array of radio telescopes in British Columbia, Canada. The Astronomer’s Telegram is a bulletin board of observations posted by accredited researchers, however these observations haven’t been peer reviewed and verified by independent teams. Still, the results make it the first detection of a FRB under 700 MHz. “These events have occurred during both the day and night, and their arrival times are not correlated with known on-site activities or other known sources,” stipulates Patrick Boyle, project manager for the Canadian Hydrogen Intensity Mapping Experiment (CHIME).

Hypotheses abound for the source of FRBs, including black holes, imploding pulsars, and magnetars emitting giant flares to name a few. According to a Harvard physicist, it’s not impossible that FRBs could be engines firing on alien spaceships. While scientists are working to discover the source, they have learned that FRBs cover a spread of frequencies, they seem to be coming from billions of light-years away, and the source of the bursts has to be very energetic. Solving this mystery could help further understanding of the origin of the Universe.

Dwarf galaxy mergers generate star formation

Dwarf galaxies have abundant levels of hydrogen gas, the fuel that drives star birth.

Dwarf galaxies such as the Large and Small Magellanic Clouds have abundant hydrogen gas, which plays a key role in star formation.

When two dwarf galaxies merge with one another or one dwarf galaxy merges with a larger, parent galaxy, this hydrogen gas is dispersed within the new combined galaxy, where it acts as fuel to generate the birth of new stars.

“You have this enormous reserve of star formation fuel sitting there ready to be stripped by another system,” explained Mary Putnam of Columbia University, who took part in a study on the role of hydrogen gas in galaxy mergers.

Both the Large and Small Magellanic Clouds are dwarf galaxy satellites of the much larger Milky Way. The two were in the process of merging when they were gravitationally pulled into the Milky Way’s orbit. Between them, there is enough hydrogen gas to replenish around half of the Milky Way’s star-formation fuel.

Much dimmer than their larger spiral counterparts, dwarf galaxies are filled with swirling hydrogen gas.

Led by then-Columbia graduate student Sarah Pearson, now at the Flatiron Institute‘s Center for Computational Astrophysics, a team of researchers observed two distant dwarf galaxies, NGC 4490 and NGC 4485, both located approximately 23 million light years away, to learn more about the role hydrogen gas in dwarf galaxies plays in creating new stars. NGC 4490 is several times larger than its partner.

Unlike the Magellanic Clouds, these two dwarf galaxies are not bound to a larger spiral galaxy like the Milky Way, so scientists can observe their merging without the influence of a larger parent galaxy.

By inputting data about the two dwarf galaxies into a computer simulation, the researchers modeled their merger, focusing on the subsequent expansion of their hydrogen gas over five billion years. By that time, “tails” of hydrogen gas stretched more than a million light years.

“After five billion years, 10 percent of the gas envelope still resides more than 260,000 light years from the merged remnant, suggesting it takes a very long time before all the gas falls back to the merged remnant,” Pearson said.

Over time, the gas clouds became more and more extended, thinning them out and making it easier for any nearby large galaxies to absorb them. This phenomenon likely makes it easy for the Milky Way to absorb gas from the Magellanic Clouds.

To better understand these dynamics, the researchers plan to study other pairs of dwarf galaxies.

A paper on the study has been published in Monthly Notices of the Royal Astronomical Society.

Distant star caught devouring planet

Researchers have finally observed a star devouring a planet.

For the first time in history astronomers have witnessed a star devouring a planet, a new study published in the Astronomical Journal reports.

This discovery comes from a team of international scientists who used NASA’s Chandra X-Ray Observatory to capture the event, which took place 450 light years from Earth.

They believe a large star known as RW Aur A swallowed a pair of newborn planets that smashed into each other before collapsing down into the fiery body’s rotating disk.

The team first took note RW Aur A some 80 years ago. Since that time, they have noted that it sits in the constellation Taurus-Auriga and is part of a binary system with another star that weighs as much as the sun.

However, what makes it particularly interesting is that it goes through a pattern where it dims for extended periods of time before slowly brightening again.

To explain its recent dimming, the team in the new study took a closer look at the star. They found that it may have gotten blocked by a thick cloud of gas and dust created by two planets smashing together and then falling into the star. That would have blocked out its light.

While computer models have long predicted that young stars can devour planets, this is the first scientists have observed such an event.

“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,” said lead author Hans Moritz Guenther, a researcher at the Massachusetts Institute of Technology, according to Tech Times.

This new information is important because, not only does it mark a never-before-seen event, it could explain previous dimming episodes as well. For example, if two planets or the remains of past collisions crashed into each other it may have created debris that spun off on rogue orbits.

The new finding marks a brand new phenomenon. Researchers hope they can shed more light on it in the future.

“Computer simulations have long predicted that planets can fall into a young star, but we have never before observed that,” added Guenther, according to Science Daily. “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.”

Passing star may have perturbed outer solar system

Orbits of outer solar system objects are warped and distorted.

A star that passed close to our solar system several billion years ago may have perturbed outer solar system objects, according to a new study based on computer simulations led by Susanne Pfalzner of the Max Planck Institute for Radio Astronomy in Bonn, Germany.

Many dwarf planets and smaller Trans-Neptunian Objects (TNOs) beyond the orbit of Pluto have extremely inclined, eccentric orbits, which scientists are hard pressed to explain. For example, dwarf planet Sedna takes 11,400 years to complete a single orbit around the Sun.

Additionally, the outer solar system is emptier than researchers think it should be.

Although Neptune orbits further from the Sun than Uranus, it is more massive, posing yet another puzzle.

These anomalies led researchers to propose a rogue star passed close to the solar system in its early days, in the process scattering thousands of distant, icy worlds into unusual positions and orbits.

“You could well have a hybrid scenario, where the movement of the planets is responsible for the things we find in the inner solar system, like the low mass of Mars, and a flyby [is responsible] for the properties of the outer solar system,” Pfalzner said.

Using data on the behavior of young stars, the researchers conducted a computer simulation of a stellar flyby to determine whether the passage of a rogue star could have caused the current arrangement of the outer solar system.

According to the simulation, the chances of a star having done this over a period of one billion years are approximately one in four, meaning this likely occurred at some point in the solar system’s early years.

Specifically, the simulation determined that a star with a mass similar to that of our Sun could have created the dynamics seen in the outer solar system if it passed within 80 to 100 astronomical units (AU, with one AU equal to the average Earth-Sun distance or 93 million miles) while the system was still forming.

During its passage, the star could have flung thousands of tiny, icy worlds beyond Pluto into interstellar space, leaving the outer solar system with the empty regions it has today.

The researchers plan to further test their theory by adding more detail to their computer simulations.

A paper on their findings has been accepted for publication in the Astrophysical Journal.