Month: June 2018

Planet Formation Starts Before Star Reaches Maturity

A European team of astronomers has discovered that dust particles around a star already coagulate before the star is fully grown. Dust particle growth is the first step in the formation of planets. The researchers from the Netherlands, Sweden and Denmark publish their findings in Nature Astronomy.

In recent years, astronomers have discovered numerous planetary systems around other stars. Almost every star is likely to have at least one planet orbiting it. Some of the major questions are centered around how planetary systems form and how this process leads to the observed diversity of planets in numbers and masses. The results of a European research project suggest that planet formation starts very early in the star formation process.

The researchers used the Atacama Large Millimeter Array for their discovery. ALMA is a collection of 66 linked radio telescopes spread over 16 kilometer in the Atacama desert in Chile. The researchers pointed the telescope toward TMC1A, a still developing star in the constellation Taurus (the Bull).

The astronomers saw a striking lack of carbon monoxide radiation in a disc-shaped area near the star. They suspected that the radiation was blocked by big dust particles. Using numerical models, they could demonstrate that indeed the dust particles in the young protoplanetary disk have probably grown from a thousandth of a millimeter to a millimeter.

Lead researcher Daniel Harsono (Leiden University, the Netherlands) explains why this is so surprising: “The results indicate that planets already start forming while the star is still developing. The star is only half to three-quarters of its final mass. This is new.”

Per Bjerkeli (Chalmers University, Sweden) highlights the implication of early grain growth: “It can be an explanation for the formation of giant planets that are comparable to Jupiter and Saturn. Only early protoplanetary discs contain sufficient mass to form giant planets.”

Co-researcher Matthijs van der Wiel (ASTRON, Netherlands Institute for Radio Astronomy) is pleased with the clear and unambiguous observations. “This early particle growth could be an exception, of course. Maybe this young disk is very special.”

In the future, the researchers want to look for tell-tale signs of planet formation around other protostars in similar manner. Ultimately, the astronomers want to know more about when and how planets are formed.

Researchers Discover Volcanic Heat as Source Under Antarctic Glacier

A researcher from the University of Rhode Island’s Graduate School of Oceanography and five other scientists have discovered an active volcanic heat source beneath the Pine Island Glacier in Antarctica.

The discovery and other findings, which are critical to understanding the stability of the West Antarctic Ice Sheet, of which the Pine Island Glacier is a part, are published in the paper, “Evidence of an active volcanic heat source beneath the Pine Island Glacier,” in the latest edition of Nature Communications.

Assistant Professor Brice Loose of Newport, a chemical oceanographer at GSO and the lead author, said the paper is based on research conducted during a major expedition in 2014 to Antarctica led by scientists from the United Kingdom. They worked aboard an icebreaker, the RRS James Clark Ross, from January to March, Antarctica’s summer.

“We were looking to better understand the role of the ocean in melting the ice shelf,” Loose said. “I was sampling the water for five different noble gases, including helium and xenon. I use these noble gases to trace ice melt as well as heat transport. Helium-3, the gas that indicates volcanism, is one of the suite of gases that we obtain from this tracing method.

“We weren’t looking for volcanism, we were using these gases to trace other actions,” he said. “When we first started seeing high concentrations of helium-3, we thought we had a cluster of bad or suspicious data.”

The West Antarctic Ice Sheet lies atop a major volcanic rift system, but there had been no evidence of current magmatic activity, the URI scientist said. The last such activity was 2,200 years ago, Loose said. And while volcanic heat can be traced to dormant volcanoes, what the scientists found at Pine Island was new.

Southwest China Builds High Altitude Cosmic-Ray Observatory

Construction has begun on a large, high altitude cosmic-ray observatory in the Ganzi Tibetan Autonomous Prefecture, Southwest China’s Sichuan Province on Tuesday, which is expected to become one of the world’s four biggest research institutes in the field.

The observatory will focus on exploring the origin of cosmic rays which “is the only sample of material obtained by humans from deep inside the universe,” Xinhua reported, citing Cao Zhen, chief expert on the project.

The project, Large High Altitude Air Shower Observatory (LHAASO), was approved by the National Development and Reform Commission in December 2015 with an estimated budget of 1.2 billion yuan ($187.2 million), and is expected to be completed by 2021, Xinhua News Agency reported.

Discovered in 1912, many things about cosmic rays remain a mystery. Cosmic rays are high energy particles that rain down on the Earth from beyond the solar system. Carrying information about the origins of the universe, celestial bodies and solar activities, it is considered a valuable scientific resource for space exploration.

The Chinese Academy of Sciences (CAS) and the government of Sichuan Province are collaborating on the project, together with 20 Chinese universities and research institutes and hundreds of scientists from China and foreign countries including Italy, France and Russia, Xinhua News Agency reported.

When completed, the observatory will be one of the four biggest cosmic-ray observatories in the world. The other three are located in South America, the South Pole and Europe.

It is also expected to be more sensitive in detecting gamma rays and have a wider range of measuring cosmic rays than any other observatory in the world.

‘Red Nuggets’ Are Galactic Gold For Astronomers

‘Red nuggets’ are galactic gold for astronomersAbout a decade ago, astronomers discovered a population of small, but massive galaxies called “red nuggets.” A new study using NASA’s Chandra X-ray Observatory indicates that black holes have squelched star formation in these galaxies and may have used some of the untapped stellar fuel to grow to unusually massive proportions.

Red nuggets were first discovered by the Hubble Space Telescope at great distances from Earth, corresponding to times only about three or four billion years after the Big Bang. They are relics of the first massive galaxies that formed within only one billion years after the Big Bang. Astronomers think they are the ancestors of the giant elliptical galaxies seen in the local Universe. The masses of red nuggets are similar to those of giant elliptical galaxies, but they are only about a fifth of their size.

While most red nuggets merged with other galaxies over billions of years, a small number managed to slip through the long history of the cosmos untouched. These unscathed red nuggets represent a golden opportunity to study how the galaxies, and the supermassive black hole at their centers, act over billions of years of isolation.

For the first time, Chandra has been used to study the hot gas in two of these isolated red nuggets, MRK 1216, and PGC 032673. They are located only 295 million and 344 million light years from Earth respectively, rather than billions of light years for the first known red nuggets. This X-ray emitting hot gas contains the imprint of activity generated by the supermassive black holes in each of the two galaxies.

“These galaxies have existed for 13 billion years without ever interacting with another of its kind,” said Norbert Werner of MTA-Eötvös University Lendület Hot Universe and Astrophysics Research Group in Budapest, Hungary, who led the study. “We are finding that the black holes in these galaxies take over and the result is not good for new stars trying to form.”

Astronomers have long known that the material falling towards black holes can be redirected outward at high speeds due to intense gravitational and magnetic fields. These high-speed jets can tamp down the formation of stars. This happens because the blasts from the vicinity of the black hole provide a powerful source of heat, preventing the galaxy’s hot interstellar gas from cooling enough to allow large numbers of stars to form.

The temperature of the hot gas is higher in the center of the MRK 1216 galaxy compared to its surroundings, showing the effects of recent heating by the black hole. Also, radio emission is observed from the center of the galaxy, a signature of jets from black holes. Finally, the X-ray emission from the vicinity of the black hole is about a hundred million times lower than a theoretical limit on how fast a black hole can grow—called the “Eddington limit”—where the outward pressure of radiation is balanced by the inward pull of gravity. This low level of X-ray emission is typical for black holes producing jets. All these factors provide strong evidence that activity generated by the central supermassive black holes in these red nugget galaxies is suppressing the formation of new stars.

The black holes and the hot gas may have another connection. The authors suggest that much of the black hole mass may have accumulated from the hot gas surrounding both galaxies. The black holes in both MRK 1216 and PGC 032873 are among the most massive known, with estimated masses of about five billion times that of the Sun, based on optical observations of the speeds of stars near the galaxies’ centers. Furthermore, the masses of the MRK 1216 black hole and possibly the one in PGC 032873 are estimated to be a few percent of the combined masses of all the stars in the central regions of the galaxies, whereas in most galaxies, the ratio is about ten times less.

“Apparently, left to their own devices, black holes can act a bit like a bully,” said co-author Kiran Lakhchaura, also of MTA-Eötvös University.

“Not only do they prevent new stars from forming,” said co-author Massimo Gaspari, an Einstein fellow from Princeton University, “they may also take some of that galactic material and use it to feed themselves.”

In addition, the hot gas in and around PGC 032873 is about ten times fainter than the hot gas around MRK 1216. Because both galaxies appear to have evolved in isolation over the past 13 billion years, this difference might have arisen from more ferocious outbursts from PGC 032873’s black hole in the past, which blew most of the hot gas away.

“The Chandra data tell us more about what the long, solitary journey through cosmic time has been like for these red nugget galaxies,” said co-author Rebecca Canning of Stanford University. “Although the galaxies haven’t interacted with others, they’ve shown plenty of inner turmoil.”

A paper describing these results in the latest issue of the Monthly Notices of the Royal Astronomical Society journal and is available online.

Einstein Proved Right In Another Galaxy

An international team of astronomers have made the most precise test of gravity outside our own solar system.

By combining data taken with NASA’s Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope, their results show that gravity in this galaxy behaves as predicted by Albert Einstein’s general theory of relativity, confirming the theory’s validity on galactic scales.

In 1915 Albert Einstein proposed his general theory of relativity (GR) to explain how gravity works. Since then GR has passed a series of high precision tests within the solar system, but there have been no precise tests of GR on large astronomical scales.

It has been known since 1929 that the Universe is expanding, but in 1998 two teams of astronomers showed that the Universe is expanding faster now than it was in the past. This surprising discovery—which won the Nobel Prize in 2011—cannot be explained unless the Universe is mostly made of an exotic component called dark energy. However, this interpretation relies on GR being the correct theory of gravity on cosmological scales. Testing the long distance properties of gravity is important to validate our cosmological model.

A team of astronomers, led by Dr. Thomas Collett of the Institute of Cosmology and Gravitation at the University of Portsmouth, used a nearby galaxy as a gravitational lens to make a precise test of gravity on astronomical length scales.

Dr. Collett said: “General Relativity predicts that massive objects deform space-time, this means that when light passes near another galaxy the light’s path is deflected. If two galaxies are aligned along our line of sight this can give rise to a phenomenon, called strong gravitational lensing, where we see multiple images of the background galaxy. If we know the mass of the foreground galaxy, then the amount of separation between the multiple images tells us if General Relativity is the correct theory of gravity on galactic scales.”

A few hundred strong gravitational lenses are known, but most are too distant to precisely measure their mass, so they can’t be used to accurately test GR. However, the galaxy ESO325-G004 is amongst the closest lenses, at 500 million light years from Earth.

Dr. Collett continues: “We used data from the Very Large Telescope in Chile to measure how fast the stars were moving in E325—this let us infer how much mass there must be in E325 to hold these stars in orbit. We then compared this mass to the strong lensing image separations that we observed with the Hubble Space telescope and the result was just what GR predicts with 9 per cent precision. This is the most precise extrasolar test of GR to date, from just one galaxy.”

“The Universe is an amazing place providing such lenses which we can then use as our laboratories,” adds team member Professor Bob Nichol, Director of the Institute of Cosmology and Gravitation. “It is so satisfying to use the best telescopes in the world to challenge Einstein, only to find out how right he was.”

The research is published today in the journal Science.

NASA Study Solves Glacier Puzzle

A new NASA study explains why the Tracy and Heilprin glaciers, which flow side by side into Inglefield Gulf in northwest Greenland, are melting at radically different rates.

Using ocean data from NASA’s Oceans Melting Greenland (OMG) campaign, the study documents a plume of warm water flowing up Tracy’s underwater face, and a much colder plume in front of Heilprin. Scientists have assumed plumes like these exist for glaciers all around Greenland, but this is the first time their effects have been measured.

The finding highlights the critical role of oceans in glacial ice loss and their importance for understanding future sea level rise. A paper on the research was published June 21 in the journal Oceanography.

Tracy and Heilprin were first observed by explorers in 1892 and have been measured sporadically ever since. Even though the adjoining glaciers experience the same weather and ocean conditions, Heilprin has retreated upstream less than 2.5 miles (4 kilometers) in 125 years, while Tracy has retreated more than 9.5 miles (15 kilometers). That means Tracy is losing ice almost four times faster than its next-door neighbor.

This is the kind of puzzle OMG was designed to explain. The five-year campaign is quantifying ice loss from all glaciers that drain the Greenland Ice Sheet with an airborne survey of ocean and ice conditions around the entire coastline, collecting data through 2020. OMG is making additional boat-based measurements in areas where the seafloor topography and depths are inadequately known.

About a decade ago, NASA’s Operation IceBridge used ice-penetrating radar to document a major difference between the glaciers: Tracy is seated on bedrock at a depth of about 2,000 feet (610 meters) below the ocean surface, while Heilprin extends only 1,100 feet (350 meters) beneath the waves.

Scientists would expect this difference to affect the melt rates, because the top ocean layer around Greenland is colder than the deep water, which has traveled north from the midlatitudes in ocean currents. The warm water layer starts about 660 feet (200 meters) down from the surface, and the deeper the water, the warmer it is. Naturally, a deeper glacier would be exposed to more of this warm water than a shallower glacier would.

When OMG Principal Investigator Josh Willis of NASA’s Jet Propulsion Laboratory in Pasadena, California, looked for more data to quantify the difference between Tracy and Heilprin, “I couldn’t find any previous observations of ocean temperature and salinity in the fjord at all,” he said. There was also no map of the seafloor in the gulf.

OMG sent a research boat into the Inglefield Gulf in the summer of 2016 to fill in the data gap. The boat’s soundings of ocean temperature and salinity showed a river of meltwater draining out from under Tracy. Because freshwater is more buoyant than the surrounding seawater, as soon as the water escapes from under the glacier, it swirls upward along the glacier’s icy face. The turbulent flow pulls in surrounding subsurface water, which is warm for a polar ocean at about 33 degrees Fahrenheit (0.5 degree Celsius). As it gains volume, the plume spreads like smoke rising from a smokestack.

“Most of the melting happens as the water rises up Tracy’s face,” Willis said. “It eats away at a huge chunk of the glacier.”

Heilprin also has a plume, but its shallower depth limits the plume’s damage in two ways: the plume has a shorter distance to rise and gathers less seawater; and the shallow seawater it pulls in has a temperature of only about 31 degrees Fahrenheit (minus 0.5 degree Celsius). As a result, even though Heilprin is a bigger glacier and more water drains from underneath it than from Tracy, its plume is smaller and colder.

The study produced another surprise by first mapping a ridge, called a sill, only about 820 feet (250 meters) below the ocean surface in front of Tracy, and then proving that this sill did not keep warm water from the ocean depths away from the glacier. “In fact, quite a lot of warm water comes in from offshore, mixes with the shallower layers and comes over the sill,” Willis said. Tracy’s destructive plume is evidence of that.

Planetary Nebula Lasers

Astronomical masers (the radio wavelength analogs of lasers) were first identified in space over fifty years ago and have since been seen in many locations; astronomical lasers have since been seen as well. Some of the most spectacular masers are found in regions of active star formation; in one case the region radiates as much energy in a single spectral line as does our Sun in its entire visible spectrum. Typically the maser radiation comes from molecules like water or OH that are excited by collisions and the radiation environment around young stars. In 1989, maser emission from atoms of atomic hydrogen gas was discovered around the star MWC349.

This remarkable source has since been found to emit lines at infrared wavelengths short enough to qualify them as being genuine lasers (not just masers). The object has been carefully modeled and the detailed conditions producing the lasers and masers have been determined: the lines arise predominantly in a dense disk of ionized gas seen nearly edge-on. Since the initial discovery, despite many searches, no other source has been found that is as complex and dramatic in its emission as is MWC349, although several other cases of weak hydrogen masers have been found.

CfA astronomer Rodolfo Montez was part of a group of fifteen astronomers using the Herschel Space Observatory to study planetary nebulae. They unexpectedly discovered twelve far infrared hydrogen laser lines in one of them, the nebula Menzel 3. Although weak compared to other atomic lines in the nebula, the hydrogen lines are much stronger than in any other known planetary nebula and stronger than was expected. Their relative strengths lines show that they cannot be coming from the normal ionized gas found in planetary nebulae, but rather from conditions that suggest high densities or some unusual effects.

The line ratios are very similar to those in MWC349, leading to the conclusion that they are lasers. Since Menzel 3 (like MWC349) has a disk being viewed edge-on and a bipolar outflow, the physical conditions seem to support this conclusion. The new result adds one more natural laser to a short cosmic list, but also adds a mystery: the radio (maser) lines in hydrogen in MWC349 and other sources are very strong emitters, yet no masers have been seen in Menzel 3. There is clearly more to learn about about this object, and about astrophysical lasers.