Astronomy Archives

January 18, 2018 by Matt Williams

Astronomers Set the Limit for Just How Massive Neutron Stars Can Be

Artist's illustration of two merging neutron stars. The narrow beams represent the gamma-ray burst while the rippling spacetime grid indicates the isotropic gravitational waves that characterize the merger. Swirling clouds of material ejected from the merging stars are a possible source of the light that was seen at lower energies. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet

In February of 2016, scientists working at the Laser Interferometer Gravitational-Wave Observatory (LIGO) made history when they announced the first-ever detection of gravitational waves. Since that time, the study of gravitational waves has advanced considerably and opened new possibilities into the study of the Universe and the laws which govern it.

For example, a team from the University of Frankurt am Main recently showed how gravitational waves could be used to determine how massive neutron stars can get before collapsing into black holes. This has remained a mystery since neutron stars were first discovered in the 1960s. And with an upper mass limit now established, scientists will be able to develop a better understanding of how matter behaves under extreme conditions.

The study which describes their findings recently appeared in the scientific journal The Astrophysical Journal Letters under the title “Using Gravitational-wave Observations and Quasi-universal Relations to Constrain the Maximum Mass of Neutron Stars“. The study was led by Luciano Rezzolla, the Chair of Theoretical Astrophysics and the Director of the Institute for Theoretical Physics at the University of Frankfurt, with assistance provided by his students, Elias Most and Lukas Wei.

*Collisions of neutron stars produce powerful gamma-ray bursts – and heavy elements like gold. Credit: Dana Berry, SkyWorks Digital, Inc.*

For the sake of their study, the team considered recent observations made of the gravitational wave event known as GW170817. This event, which took place on August 17th, 2017, was the sixth gravitational wave to be discovered by the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo Observatory. Unlike previous events, this one was unique in that it appeared to be caused by the collision and explosion of two neutron stars.

And whereas other events occurred at distances of about a billion light years, GW170817 took place only 130 million light years from Earth, which allowed for rapid detection and research. In addition, based on modeling that was conducted months after the event (and using data obtained by the Chandra X-ray Observatory) the collision appeared to have left behind a black hole as a remnant.

The team also adopted a “universal relations” approach for their study, which was developed by researchers at Frankfurt University a few years ago. This approach implies that all neutron stars have similar properties which can be expressed in terms of dimensionless quantities. Combined with the GW data, they concluded that the maximum mass of non-rotating neutron stars cannot exceed 2.16 solar masses.

*Artist’s impression of gravitational-wave emissions from a collapsing star. Credit: aktuelles.uni-frankfurt.de*

As Professor Rezzolla explained in a University of Frankfurt press release:

“The beauty of theoretical research is that it can make predictions. Theory, however, desperately needs experiments to narrow down some of its uncertainties. It’s therefore quite remarkable that the observation of a single binary neutron star merger that occurred millions of light years away combined with the universal relations discovered through our theoretical work have allowed us to solve a riddle that has seen so much speculation in the past.”

This study is a good example of how theoretical and experimental research can coincide to produce better models ad predictions. A few days after the publication of their study, research groups from the USA and Japan independently confirmed the findings. Just as significantly, these research teams confirmed the studies findings using different approaches and techniques.

In the future, gravitational-wave astronomy is expected to observe many more events. And with improved methods and more accurate models at their disposal, astronomers are likely to learn even more about the most mysterious and powerful forces at work in our Universe.

Further Reading: Goethe University Frankfurt am Main, The Astrophysical Journal Letters

January 18, 2018 by Matt Williams

Physicists Have Created an Artificial Gamma Ray Burst in the Lab

Artist's impression of a gamma-ray burst, showing the two intense beams of relativistic matter emitted by the black hole. To be visible from Earth, the beams must be pointing directly towards us. Credit : NASA/Swift/Mary Pat Hrybyk-Keith and John Jones

On July 2nd, 1967, the U.S. Vela 3 and 4 satellites noticed something rather perplexing. Originally designed to monitor for nuclear weapons tests in space by looking for gamma radiation, these satellites picked up a series of gamma-ray bursts (GRBs) coming from deep space. And while decades have passed since the “Vela Incident“, astronomers are still not 100% certain what causes them.

One of the problems has been that until now, scientists have been unable to study gamma ray bursts in any real capacity. But thanks to a new study by an international team of researchers, GRBs have been recreated in a laboratory for the first time. Because of this, scientists will have new opportunities to investigate GRBs and learn more about their properties, which should go a long away towards determining what causes them.

The study, titled “Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam“, was recently published in the Physical Review Letters. The study was led by Jonathon Warwick from Queen’s University Belfast and included members from the SLAC National Accelerator Laboratory, The John Adams Institute for Accelerator Science, the Rutherford Appleton Laboratory, and multiple universities.

*Artist’s impression of a gamma ray burst in space. Credit: ESO/A. Roquette*

Until now, the study of GRBs have been complicated by two major issues. On the one hand, GRBs are very short lived, lasting for only seconds at a time. Second, all detected events have occurred in distant galaxies, some of which were billions of light-years away. Nevertheless, there are a few theories as to what could account for them, ranging from the formation of black holes and collisions between neutron stars to extra-terrestrial communications.

For this reason, investigating GRBs is especially appealing to scientists since they could reveal some previously-unknown things about black holes. For the sake of their study, the research team approached the question of GRBs as if they were related to the emissions of jets of particles released by black holes. As Dr. Gianluca Sarri, a lecturer at Queen’s University Belfast, explained in a recent op-ed piece with The Conversation:

“The beams released by the black holes would be mostly composed of electrons and their “antimatter” companions, the positrons… These beams must have strong, self-generated magnetic fields. The rotation of these particles around the fields give off powerful bursts of gamma ray radiation. Or, at least, this is what our theories predict. But we don’t actually know how the fields would be generated.”

With the assistance of their collaborators in the US, France, the UK and Sweden, the team from Queen’s University Belfast relied on the Gemini laser, located at the Rutherford Appleton Laboratory in the UK. With this instrument, which is one of the most powerful lasers in the world, the international collaboration sought to create the first small scale replica of GRBs.

*Artist’s impression of a supermassive black hole emitting powerful jets of charged particles. Credit: Robin Dienel/Carnegie Institution for Science*

By shooting this laser onto a complex target, the team was able to create miniature versions of these ultra-fast astrophysical jets, which they recorded to see how they behaved. As Dr. Sarri indicated:

“In our experiment, we were able to observe, for the first time, some of the key phenomena that play a major role in the generation of gamma ray bursts, such as the self-generation of magnetic fields that lasted for a long time. These were able to confirm some major theoretical predictions of the strength and distribution of these fields. In short, our experiment independently confirms that the models currently used to understand gamma ray bursts are on the right track.”

This experiment was not only important for the study of GRBs, it could also advance our understanding about how different states of matter behave. Basically, almost all phenomena in nature come down to the dynamics of electrons, as they are much lighter than atomic nuclei and quicker to respond to external stimuli (such as light, magnetic fields, other particles, etc).

“But in an electron-positron beam, both particles have exactly the same mass, meaning that this disparity in reaction times is completely obliterated,” said Dr. Sarri. “This brings to a quantity of fascinating consequences. For example, sound would not exist in an electron-positron world.”

In addition, there is the aforementioned argument that GRBs could in fact be evidence of Extra-Terrestrial Intelligence (ETI). In the Search for Extra-Terrestrial Intelligence (SETI), scientists look for electromagnetic signals that do not appear to have natural explanations. By knowing more about different types of electromagnetic bursts, scientists could be better able to isolate those for which there are no known causes. As Dr. Sarri put it:

“Of course, if you put your detector to look for emissions from space, you do get an awful lot of different signals. If you really want to isolate intelligent transmissions, you first need to make sure all the natural emissions are perfectly known so that they can excluded. Our study helps towards understanding black hole and pulsar emissions, so that, whenever we detect anything similar, we know that it is not coming from an alien civilization.”

Much like research into gravitational waves, this study serves as an example of how phenomena that were once beyond our reach is now open to study. And much like gravitational waves, research into GRBs is likely to yield some impressive returns in the coming years!

Further Reading: The Conversation, Physical Review Letters

January 17, 2018 by Matt Williams

James Webb Wraps up 3 Months in the Freezer. It’s Ready for Space

The James Webb Space Telescope inside a cleanroom at NASA’s Johnson Space Center in Houston. Credit: NASA/JSC

When the James Webb Space Telescope finally takes to space, it will study some of the most distant objects in the Universe, effectively looking back in time to see the earliest light of the cosmos. It will also study extra-solar planets around nearby stars and even bodies within the Solar System. In this respect, the JWST is the natural successor to Hubble and other pioneering space telescopes.

It is therefore understandable why the world is so eager for the JWST to be launched into space (which is now scheduled to take place in 2019). And recently, the telescope passed another major milestone along the road towards deployment. After spending three months in a chamber designed to simulate the temperatures and vacuum conditions of space, the JWST emerged and was given a clean bill of health.

The tests took place inside Chamber A, a thermal vacuum testing facility located at the Johnson Space Center in Houston, Texas. This chamber was built back in 1965 as part of NASA’s race to the Moon, where it conducted tests to ensure that the Apollo command and service modules were space-worthy. Beginning in mid-July, the telescope was put into the chamber and subjected to temperatures ranging from 20 to 40 K (-253 to -233 °C; 423 to 387 °F).

*NASA’s James Webb Space Telescope sits in Chamber A at NASA’s Johnson Space Center in Houston awaiting the colossal door to close in July 2017 for cryogenic testing. Credits: NASA/Chris Gunn*

Once the temperature and vacuum conditions were just right, a team of NASA engineers began testing the alignment of the JWST’s 18 primary mirror segments to make sure they would act as a single, 6.5-meter telescope. As Bill Ochs – the James Webb telescope project manager at NASA’s Goddard Space Flight Center – indicated to ArsTechnica, this latest test has shown that the telescope is indeed space-worthy.

“We now have verified that NASA and its partners have an outstanding telescope and set of science instruments,” he said. “We are marching toward launch.”

The team of engineers also tested the JWST’s guidance and optical systems by simulating the light of a distant star. Not only was the telescope able to detect the light, its optical systems were able to process it. The telescope was also able to track the simulated star’s movement, which demonstrated that the JWST will be able to acquire and hold research targets once it is in space.

Many tests are still needed before the JWST can take to space next year. These will be conducted at Northrop Grumman’s company headquarters in Los Angeles, where the telescope will be transported after leaving the Johnson Space Center in late January or early February. Once there, the optical instrument will mated to the spacecraft and sunshield to complete the construction of the telescope.

*The sunshield test unit on NASA’s James Webb Space Telescope is unfurled for the first time. Credit: NASA*

These tests are necessary since NASA will be hard-pressed to service the telescope once it is in space. This is due to the fact that it will be operating at the Earth-Sun L2 Lagrange Point (which will place farther away from Earth than the Moon) for a minimum of five years. At this distance, any servicing missions will be incredibly difficult, time-consuming and expensive to mount.

However, once the JWST has passed its entire battery of tests and NASA is satisfied it is ready to take to space, it will be shipped off to the Guiana Space Center in Kourou, French Guiana. Once there, it will launch aboard a European Space Agency (ESA) Ariane V booster. Originally, this was scheduled to take place in October of 2017, but is now expected to take place no earlier than Spring of 2018.

When the James Webb Space Telescope is operational, it is expected to reveal some truly amazing things about our Universe. In addition to looking farther into space than any previous telescope (and further back in time), its other research goals include studying nearby exoplanets in unprecedented detail, circumstellar debris disks, supermassive black holes at the centers of galaxies, and even searching for life in the Solar System by examining Jupiter’s moons.

For this reason, NASA can be forgiven for pushing the launch back to make sure everything is in working order. But of course, we can be forgiven for wanting to see it launched as soon as possible! There are mysteries out there that are just waiting to be revealed, and some amazing scientific finds that need to be followed up on.

In the meantime, be sure to check out this video about the JWST, courtesy of NASA:

Further Reading: ArsTechnica, NASA

January 12, 2018May 11, 2018 by Matt Williams

Astronomers Figure Out How Black Holes Can Blast Out Relativistic Jets of Material Across Light Years of Space

Artist's impression of the relativistic jet emanating from a black hole. Credit: Northwestern University

Black holes have been an endless source of fascination ever since Einstein’s Theory of General Relativity predicted their existence. In the past 100 years, the study of black holes has advanced considerably, but the awe and mystery of these objects remains. For instance, scientists have noted that in some cases, black holes have massive jets of charged particles emanating from them that extend for millions of light years.

These “relativistic jets” – so-named because they propel charged particles at a fraction of the speed of light – have puzzled astronomers for years. But thanks to a recent study conducted by an international team of researchers, new insight has been gained into these jets. Consistent with General Relativity, the researchers showed that these jets gradually precess (i.e. change direction) as a result of space-time being dragged into the rotation of the black hole.

Their study, titled “Formation of Precessing Jets by Tilted Black Hole Discs in 3D General Relativistic MHD Simulations“, recently appeared in the Monthly Notices of the Royal Astronomical Society. The team consisted of members from the Anton Pannekoek Institute for Astronomy at the University of Amsterdam and a professor from the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) at Northwestern University.

For the sake of their study, the team conducted simulations using the Blue Waters supercomputer at the University of Illinois. The simulations they conducted were the first ever to model the behavior of relativistic jets coming from Supermassive Black Holes (SMBHs). With close to a billion computational cells, it was also the highest-resolution simulation of an accreting black hole ever achieved.

As Alexander Tchekhovskoy, an assistant professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences, explained in a recent Northwestern Now press release:

“Understanding how rotating black holes drag the space-time around them and how this process affects what we see through the telescopes remains a crucial, difficult-to-crack puzzle. Fortunately, the breakthroughs in code development and leaps in supercomputer architecture are bringing us ever closer to finding the answers.”

Much like all Supermassive Black Holes, rapidly spinning SMBHs regularly engulf (aka. accrete) matter. However, rapidly spinning black holes are also known for the way they emit energy in the form of relativistic jets. The matter that feeds these black holes forms a rotating disk around them – aka. an accretion disk – which is characterized by hot, energized gas and magnetic field lines.

It is the presence of these field lines that allows black holes to propel energy in the form of these jets. Because these jets are so large, they are easier to study than the black holes themselves. In so doing, astronomers are able to understand how quickly the direction of these jets change, which reveals things about the rotation of the black holes themselves – such as the orientation and size of their rotating disks.

Advanced computer simulations are necessary when it comes to the study of black holes, largely because they are not observable in visible light and are typically very far away. For instance, the closest SMBH to Earth is Sagittarius A*, which is located about 26,000 light-years away at the center of our galaxy. As such, simulations are the only way to determine how a highly complex system like a black hole operates.

In previous simulations, scientists operated under the assumption that black hole disks were aligned. However, most SMBHs have been found to have tilted disks – i.e. the disks rotate around a separate axis than the black hole itself. This study was therefore seminal in that it showed how disks can change direction relative to their black hole, leading to precessing jets that periodically change their direction.

This was previously unknown because of the incredibly amount of computing power that is needed to construct 3-D simulations of the region surrounding a rapidly spinning black hole. With the support of a National Science Foundation (NSF) grant, the team was able to achieve this by using the Blue Waters, one of the largest supercomputers in the world.

*Detection of an unusually bright X-Ray flare from Sagittarius A*, a supermassive black hole in the center of the Milky Way galaxy. Credit: NASA/CXC/Stanford/I. Zhuravleva et al.*

With this supercomputer at their disposal, the team was able to construct the first black hole simulation code, which they accelerated using graphical processing units (GPUs). Thanks to this combination, the team was able to carry out simulations that had the highest level of resolution ever achieved – i.e. close to a billion computational cells. As Tchekhovskoy explained:

“The high resolution allowed us, for the first time, to ensure that small-scale turbulent disk motions are accurately captured in our models. To our surprise, these motions turned out to be so strong that they caused the disk to fatten up and the disk precession to stop. This suggests that precession can come about in bursts.”

The precession of relativistic jets could explain why light fluctuations have been observed coming from around black holes in the past – which are known as quasi-periodic oscillations (QPOs). These beams, which were first discovered by Michiel van der Klis (one of the co-authors on the study), operate in much the same way as a quasar’s beams, which appear to have a strobing effect.

This study is one of many that is being conducting on rotating black holes around the world, the purpose of which is to gain a better understanding about recent discoveries like gravitational waves, which are caused by the merger of black holes. These studies are also being applied to observations from the Event Horizon Telescope, which captured the first images of Sagittarius A*’s shadow. What they will reveal is sure to excite and amaze, and potentially deepen the mystery of black holes.

In the past century, the study of black holes has advanced considerably – from the purely theoretical, to indirect studies of the effects they have on surrounding matter, to the study of gravitational waves themselves. Perhaps one day, we might actually be able to study them directly or (if it’s not too much to hope for) peer directly inside them!

Further Reading: Northwestern Now, MNRAS

January 12, 2018 by Matt Williams

China Says it Still has Control Over Tiangong-1 and Can Decide Where It’ll Crash

An artist's illustration of China's uncrewed Tiangzhou-1 cargo ship in orbit. Credit: China Manned Space Agency

The Tiangong-1 space station has been the subject of a lot of interest lately. Though its mission was meant to end in 2013, the China National Space Agency extended its service until 2016. In September of 2017, after much speculation from the international community, the Agency acknowledged that the station’s orbit was degrading and that it would fall to Earth later in the year.

Based on updates from satellite trackers, it has been indicated that Tianglong-1 will likely reenter our atmosphere in March of 2018, with the possibility of debris making it to the surface. However, according to a statement made by a top engineer at the China Aerospace Science and Technology Corporation (CASTC), reports that the Chinese National Space Agency (CNSA) has lost control of the space station have been wildly exaggerated.

The statement came from Zhu Congpeng, a top engineer at the China Aerospace Science and Technology Corporation (CASTC). As he was quoted as saying to the Science and Technology Daily newspaper – a state-backed Chinese science journal – the CNSA is still in control of the space station, it’s reentry will be controlled, and it will not pose a threat to the environment or any population centers.

*Artist’s illustration of China’s 8-ton Tiangong-1 space station, which is expected to fall to Earth in late 2017. Credit: CMSE*

Previously, the CNSA claimed that the majority of the station would burn up in orbit, with only small pieces falling to the Earth. But according to Zhu Congpeng’s statement, when the station burns up in the atmosphere, the remaining debris will not jeopardize people, infrastructure or the environment anywhere on the surface. As Zhu Congpeng stated:

“We have been continuously monitoring Tiangong-1 and expect to allow it to fall within the first half of this year. It will burn up on entering the atmosphere and the remaining wreckage will fall into a designated area of the sea, without endangering the surface.”

As with previous missions – like the Mir space station, the Russian Progress spacecraft, and NASA’s Compton Gamma-Ray Observatory – the designated crash site is a deep-sea area in the South Pacific known as the “spacecraft cemetery”. As a further indication that the CNSA is still in control of Tiangong-1, Zhu claimed that the CNSA has been constantly monitoring the space station since the end of its mission.

“The latest bulletin shows that on December 17-24, 2017, Temple One runs on an orbit with an average height of about 286.5 kilometers (height of about 272.6 kilometers near perigee, height of about 300.4 kilometers at apogee and inclination of about 42.85 degrees), attitude stability,” he said. “There is no abnormal morphology.”

*The Aerospace Corporations predicted reentry for Tiangong-1. Credit: aerospace.org*

He also emphasized that the station’s reentry was delayed until September in order to ensure the the wreckage would fall into the South Pacific. In other words, the position of Tiangong-1 is something the Chinese have been monitoring closely, and they will continue to do so when it reenters the atmosphere this coming March. This latest statement comes on the heels of statements made by both China’s manned space engineering office and the Aerospace Corporation, which appeared to offer a different appraisal.

Back in mid-September, Wu Ping – the deputy director of China’s manned space engineering office – stated at a press conference that there was some chance that debris would land on Earth. While she was insistent that the odds of any debris surviving the passage through Earth’s atmosphere were minimal, it did suggest that the reentry would be uncontrolled.

This echoed the comprehensive report recently issued by the Aerospace Corporation, which stated that the Chinese space agency was unlikely to remain in control of Tiangong-1’s for the entirety of its reentry. Much like Wu, they also emphasized that the majority of the station would burn up on reentry and that it was unlikely that any debris would make it to the surface and cause damage.

As such, its not entirely clear if the reentry will be entirely controlled or not. But even if it should prove to be the latter, there is little reason to worry. As the Aerospace Corporation stated in their report:

“[T]he probability that a specific person (i.e., you) will be struck by Tiangong-1 debris is about one million times smaller than the odds of winning the Powerball jackpot. In the history of spaceflight, no known person has ever been harmed by reentering space debris. Only one person has ever been recorded as being hit by a piece of space debris and, fortunately, she was not injured.”

*Banxing-2 snaps Tiangong-2 and Shenzhou-11 using a fisheye camera. Credit: Chinese Academy of Sciences*

On top of that, the European Space Agency’s Inter Agency Space Debris Coordination Committee (IADC) will also be monitoring the reentry closely. They’ll also be using the occasion to conduct a test campaign designed to improve the accuracy of reentry predictions. And so far, all their predictions indicate that come March, people on Earth will be safe from falling debris.

So if you happen to live close to the equator, this coming March is sure to be an exciting time for sky-watchers! And if there’s any chance of debris landing where you live, you can sure you’ll hear about it well in advance.

Further Reading: Independent, STDaily

January 10, 2018 by Matt Williams

The Ozone Hole is Definitely Recovering

A view of Earth's atmosphere from space. Credit: NASA

The ozone layer is a integral part of what makes Earth habitable. This region of the stratosphere is responsible for absorbing the majority of the Sun’s ultraviolet radiation, thus ensuring terrestrial organisms are not irradiated. Since the 1970s, scientists became aware of a steady decline in this layer around the southern polar region, along with and a major seasonal decrease. This latter phenomena, known as the “ozone hole”, has been a major concern for decades.

Attempts to remedy this situation have focused on cutting the use of industrial chemicals, such as chlorofluorocarbons (CFCs). These efforts culminated with the signing of the Montreal Protocol in 1987, which called for the complete phasing out of ozone-depleting substances (ODSs). And according to recent study by a team of NASA scientists, the ozone hole is showing signs of significant recovery as a result.

The study, titled “Decline in Antarctic Ozone Depletion and Lower Stratospheric Chlorine Determined From Aura Microwave Limb Sounder Observations“, recently appeared in the scientific journal Geophysical Research Letters. The study was led by Susan E Strahan and co-authored by Anne R. Douglass, two research scientists with NASA Goddard’s Atmospheric Chemistry and Dynamics Laboratory.

*Artist’s impression of the Aura satellite. Credit: NASA*

For the sake of their study, the team consulted data from NASA’s Aura satellite, which has been monitoring the southern polar region since 2005. Having launched in 2004, the purpose of the Aura satellite was to conduct measurements of ozone, aerosols and key gases in the Earth’s atmosphere. And according to the readings it has gathered since 2005, the reductions in the use of CFCs has led to a 20% decrease in ozone depletion.

Simply put, CFCs are long-lived chemical compounds that are made up of carbon, chlorine, and fluorine. Since the latter half of the 20th century, they have been used in a number of industrial applications such as refrigeration (as Freon), in chemical aerosols (as propellants), and as solvents. Eventually, these chemicals rise into the stratosphere where they become subject to UV radiation and are broken down into chlorine atoms.

These chlorine atoms play havoc with the ozone layer, where they catalyze to form oxygen gas (O²). This activity begins around July during the Southern Hemisphere’s winter, when the Sun’s rays cause an increase in the catalyzing of CFC-derived chlorine and bromine atoms in the atmosphere. By September (i.e. spring in the southern hemisphere), the activity peaks, resulting on the “ozone hole” that scientists first noted in 1985.

In the past, statistical analysis studies have indicated that ozone depletion has increased since. However, this study – which was the first to use measurements of the chemical composition inside the ozone hole – indicated that ozone depletion is decreasing. What’s more, it indicated that the decrease is caused by the decline in CFC use.

As Susan Strahan explained in a recent NASA press release, “We see very clearly that chlorine from CFCs is going down in the ozone hole, and that less ozone depletion is occurring because of it.” To determine how ozone and other chemicals in the atmosphere have changed from year to year, scientists have relied on data from the Aura satellite’s Microwave Limb Sounder (MLS).

Unlike other instruments that rely on sunlight to obtain spectra from atmospheric gases, this instrument measures these gases respective microwave emissions. As a result, it can measure trace gases over Antarctica during a key time of the year – when the southern hemisphere is experiencing winter and weather in the stratosphere is calm and temperatures are low and stable.

The change in ozone levels from the beginning to the end of Southern Hemisphere’s winter (early July to mid-September) was computed daily using MLS measurements every year from 2005 to 2016. While these measurements indicated a decrease in ozone loss, Strahan and Douglass wanted to be certain reductions in the use of CFCs was what was responsible.

This they did by looking for telltale signs of hydrochloric acid in the MLS data, which chlorine will form by reacting with methane (but only when all available ozone is depleted). As Strahan explained:

“During this period, Antarctic temperatures are always very low, so the rate of ozone destruction depends mostly on how much chlorine there is. This is when we want to measure ozone loss… By around mid-October, all the chlorine compounds are conveniently converted into one gas, so by measuring hydrochloric acid we have a good measurement of the total chlorine.”

*Images from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite showing ozone fluctuations between 2010 and 2011. Credit: NASA/Rob Simmon*

Another hint came in the form of nitrous oxide levels, another long-lived gas that behaves just like CFCs in much of the stratosphere – but which is not in decline like CFCs. If CFCs in the stratosphere were decreasing, it would mean that less chlorine would be present compared to nitrous oxide. By comparing MLS measurements of hydrochloric acid and nitrous oxide each year, they determined that chlorine levels were declining by about 0.8 percent per year.

As Strahan indicated, this added up to a 20% decrease from 2005 to 2016, which was consistent with what they expected. “This is very close to what our model predicts we should see for this amount of chlorine decline,” she said. “This gives us confidence that the decrease in ozone depletion through mid-September shown by MLS data is due to declining levels of chlorine coming from CFCs. But we’re not yet seeing a clear decrease in the size of the ozone hole because that’s controlled mainly by temperature after mid-September, which varies a lot from year to year.”

This process of recovery is expected to continue as CFCs gradually leave the atmosphere, though scientists anticipate that a complete recovery will take decades. This is very good news considering that the ozone hole was discovered only about three decades ago, and ozone levels began to stabilize about a decade later. Still, as Douglass explained, a full recovery is not likely to take place until the latter half of this century:

“CFCs have lifetimes from 50 to 100 years, so they linger in the atmosphere for a very long time. As far as the ozone hole being gone, we’re looking at 2060 or 2080. And even then there might still be a small hole.”

The Montreal Protocol is often touted as an example of effective international climate action, and for good reason. The Protocol was struck thirteen years after the scientific consensus on ozone depletion was reached, and just two years after the rather alarming discovery of the ozone hole. And in the years that followed, the signatories remained committed to their goals and achieved target reductions.

In the future, it is hoped that similar action can be achieved on climate change, which has been subject to delays and resistance for many years now. But as the case of the ozone hole demonstrates, international action can address a problem before it is too late.

Further Reading: NASA

January 10, 2018November 7, 2018 by Paul M. Sutter

The Night Sky Magic of the Atacama

night sky above the atacama — Thousands of stars glitter in the black skies above the bone-dry desert of the Atacama in northern Chile. Photo credit: Gerhard Hüdepohl/atacamaphoto.com.

There’s nothing an astronomer – whether professional or amateur – loves more than a clear dark night sky away from the city lights. Outside the glare and glow and cloud cover that most of us experience every day, the night sky comes alive with a life of its own.

Thousands upon countless thousands of glittering jewels – each individual star a pinprick of light set against the velvet-smooth blackness of the deeper void. The arching band of the Milky Way, itself host to billions more stars so far away that we can only see their combined light from our vantage point. The familiar constellations, proudly showing their true character, drawing the eye and the mind to the ancient tales spun about them.

There are few places left in the world to see the sky as our ancestors did; to gaze in wonder at the celestial dome and feel the weight of billions of years of cosmic history hanging above us. Thankfully the International Dark Sky Association is working to preserve what’s left of the true night sky, and they’ve rightfully marked northern Chile to preserve for posterity.

Continue reading “The Night Sky Magic of the Atacama”

January 8, 2018January 8, 2018 by Tammy Plotner

Messier 65 – the NGC 3623 Intermediate Spiral Galaxy

Hubble image of the intermediate spiral galaxy known as Messier 65, which is located in the Leo constellation. Credit: ESA/Hubble & NASA

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the intermediate spiral galaxy known as Messier 65.

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects he initially mistook for comets. In time, he would come to compile a list of approximately 100 of these objects, hoping to prevent other astronomers from making the same mistake. This list – known as the Messier Catalog – would go on to become one of the most influential catalogs of Deep Sky Objects.

One of these objects is the intermediate spiral galaxy known as Messier 65 (aka. NGC 3623), which is located about 35 million light-years from Earth in the Leo constellation. Along with with Messier 66 and NGC 3628, it is part of a small group of galaxies known as the Leo Triplet, which makes it one of the most popular targets among amateur astronomers.

Description:

Enjoying life some 35 million light years from the Milky Way, the group known as the “Leo Trio” is home to bright galaxy Messier 65 – the westernmost of the two M objects. To the casual observer, it looks like a very normal spiral galaxy and thus its classification as Sa – but M65 is a galaxy which walks on the borderline. Why? Because of close gravitational interaction with its nearby neighbors. Who can withstand the draw of gravity?!

*The Messier 65 intermediate spiral galaxy. Credit: ESO/INAF-VST/OmegaCAM/Astro-WISE/Kapteyn Institute*

Chances are very good that Messier 65 is even quite a bit larger than we see optically as well. As E. Burbidge (et al) said in a 1961 study:

“A fragmentary rotation-curve for NGC 3623 was obtained from measures of the absorption features Ca ii X 3968 and Na I X 5893 and the emission lines [N ii] X 6583 and Ha. The measures from two outer regions are discordant if only circular velocities are assumed, and it is concluded that the measured velocity of one of these regions-the only prominent H ii region in the galaxy-has a large non-circular component. The approximate mass derived from the velocity in the outer arm relative to the center is 1.4 X 1011 M0. It is concluded that the total mass is larger than this, perhaps between 2 and 3 X 1011 M0. This would suggest that the mass-to-light ratio in solar units (photographic) for this galaxy, which is intermediate in type between Sa and Sb, lies between 10 and 20.”

But just how much interaction has been going on between the three galaxies which coexist so closely? Sometimes it takes things like studying in multicolor photometry data to understand. As Zhiyu Duan of the Chinese Academy of Sciences Astronomical Observatory indicated in a 2006 study:

“By comparing the observed SEDs of each part of the galaxies with the theoretical ones generated by instantaneous burst evolutionary synthesis models with different metallicities (Z = 0.0001, 0.008, 0.02, and 0.05), two-dimensional relative age distribution maps of the three galaxies were obtained. NGC 3623 exhibits a very weak age gradient from the bulge to the disk. This gradient is absent in NGC 3627. The ages of the dominant stellar populations of NGC 3627 and NGC 3628 are consistent, and this consistency is model independent (0.5-0.6 Gyr, Z = 0.02), but the ages of NGC 3623 are systematically older (0.7-0.9 Gyr, Z = 0.02). The results indicate that NGC 3627 and NGC 3628 have undergone synchronous evolution and that the interaction has likely triggered starbursts in both galaxies. The results indicate that NGC 3627 and NGC 3628 have undergone synchronous evolution and that the interaction has likely triggered starbursts in both galaxies. For NGC 3623, however, the weak age gradient may indicate recent star formation in its bulge, which has caused its color to turn blue. Evidence is found for a potential bar existing in the bulge of NGC 3623, and my results support the view that NGC 3623 does interact with NGC 3627 and NGC 3628.”

*Messier 65, as imaged by the Hubble Space Telescope. Credit: NASA,/ESA/Hubble Space Telescope*

So, let’s try looking at things in a slightly different color – integral-field spectroscopy. As V.L. Afanasiev (et al) said in a 2004 study:

“The mean ages of their circumnuclear stellar populations are quite different, and the magnesium overabundance of the nucleus in NGC 3627 is evidence for a very brief last star formation event 1 Gyr ago whereas the evolution of the central part of NGC 3623 looks more quiescent. In the center of NGC 3627 we observe noticeable gas radial motions, and the stars and the ionized gas in the center of NGC 3623 demonstrate more or less stable rotation. However, NGC 3623 has a chemically distinct core – a relic of a past star formation burst – which is shaped as a compact, dynamically cold stellar disk with a radius of ?250-350 pc which has been formed not later than 5 Gyr ago.”

Now, let’s take a look at that gas – and the properties for the gases that exist and co-exist in the galactic trio. As David Hogg (et al) explained in a 2001 study:

“We have studied the distribution of cool, warm, and hot interstellar matter in three of the nearest bright Sa galaxies. New X-ray data for NGC 1291, the object with the most prominent bulge, confirm earlier results that the ISM in the bulge is dominated by hot gas. NGC 3623 has a lesser amount of hot gas in the bulge but has both molecular gas and ionized hydrogen in the central regions. NGC 2775 has the least prominent bulge; its X-ray emission is consistent with an origin in X-ray binary stars, and there is a strict upper limit on the amount of molecular present in the bulge. All three galaxies have a ring of neutral hydrogen in the disk. NGC 3623 and NGC 2775 each have in addition a molecular ring coincident with the hydrogen ring. We conclude that even within the morphological class Sa there can be significant differences in the gas content of the bulge, with the more massive bulges being likely to contain hot, X-ray–emitting gas. We discuss the possibility that the X-ray gas is part of a cooling flow in which cool gas is produced in the nucleus.”

*The Leo Triplet, with M65 at the upper right, M66 at the lower right, and NGC 3628 at the upper left. Credit: Scott Anttila. Credit: Wikipedia Commons/Anttler*

Even more studies have been done to take a look a disc properties associated with M65. According to M. Bureau (et al);

“NGC 3623 (M 65) is another highly-inclined galaxy in the Leo group, but it is of much later type than NGC 3377, SABa(rs). It is part of the Leo triplet with NGC 3627 and NGC 3628 but does not appear to be interacting. NGC 3623’s kinematics an has barely been studied and observations provide a glimpse of its dynamics. The large-scale velocity reveals minor-axis rotation, in agreement with the presence of a bar. In addition, a quasi edge-on disk is present in the center, where the iso velocity contours flatten out abruptly.”

History of Observation:

Both M65 and M66 were discovered on the same night – March 1, 1780 – by Charles Messier, who described M65 as “Nebula discovered in Leo: It is very faint and contains no star.” Sir William Herschel would later observe M65 as well, describing it as “A very brilliant nebula extended in the meridian, about 12′ long. It has a bright nucleus, the light of which suddenly diminishes on its border, and two opposite very faint branches.”

However, it would be Lord Rosse who would be the first to see structure: “March 31, 1848. – A curious nebula with a bright nucleus; resolvable; a spiral or annular arrangement about it; no other portion of the nebula resolved. Observed April 1, 1848 and April 3, with the same results.”

Locating Messier 65:

Even though you might think by its apparent visual magnitude that M65 wouldn’t be visible in small binoculars, you’d be wrong. Surprisingly enough, thanks to its large size and high surface brightness, this particular galaxy is very easy to spot directly between Iota and Theta Leonis. In even 5X30 binoculars under good conditions you’ll easy see both it and M66 as two distinct gray ovals.

*Messier 65 location. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)*

A small telescope will begin to bring out structure in both of these bright and wonderful galaxies, but to get a hint at the “Trio” you’ll need at least 6″ in aperture and a good dark night. If you don’t spot them right away in binoculars, don’t be disappointed – this means you probably don’t have good sky conditions and try again on a more transparent night. The pair is well suited to modestly moonlit nights with larger telescopes.

Capture one of the Trio tonight! And here are the quick facts on this Messier Object:

Object Name: Messier 65
Alternative Designations: M65, NGC 3623, (a member of the) Leo Trio, Leo Triplet
Object Type: Type Sa Spiral Galaxy
Constellation: Leo
Right Ascension: 11 : 18.9 (h:m)
Declination: +13 : 05 (deg:m)
Distance: 35000 (kly)
Visual Brightness: 9.3 (mag)
Apparent Dimension: 8×1.5 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, M1 – The Crab Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

January 8, 2018January 8, 2018 by Matt Williams

This is the Year Internet From Space Gets Really Serious

A number companies are deploying satellites this year to create space-based internet services. Credit: AMNH.

Between 2005 and 2017, the number of people who are digitally connected increased by a factor of three and a half. In other words, the number of people with internet access went from just over 1 billion to about 3.5, from about 15% to roughly half the world’s population. And in the coming decade, it is estimated that roughly 5 billion people – that’s 70% of the world’s population – will have internet access.

Much is this growth is powered by new ways of in which internet services are being provided, which in the coming years will include space-based internet. In 2018 alone, eight new constellations of internet satellites will begin deployment to Low-Earth Orbit (LEO) and Medium-Earth Orbit (MEO). Once operational, these constellations are expected to not only increas broadband access, but also demonstrate the soundness of the business model.

For instance, SpaceX will be launching a prototype internet satellite this year, the first of a planned constellation of 4,425 satellites that will make up its Starlink Service. As part of Elon Musk’s vision to bring internet access to the entire globe (one of many he’s had in recent years!), this constellation will be deployed to altitudes of 1,110 to 1,325 km (685-823 mi) – i.e. within LEO – by 2024.

Telecom and aerospace giants Samsung and Boeing are also sending internet satellites to orbit this year. In Samsung’s case, the plan is to begin deploying the first of 4,600 satellites to LEO by 2028. Once operational, this interconnected constellation will provide a 200-GB per month service in the V band for up to 5 billion users. Boeing has similar plans for a 2,956 constellation that will provide enhanced broadband (also in the V band).

The first part of this system will consist of 1,396 satellites deployed to an altitude of 1,200 km (746 mi) within the first six years. Others companies that are getting in on the ground floor of the space-based internet trend include OneWeb, Telesat LEO, SES O3B, Iridium Next and LeoSat. Each of them have plans to send between a few dozen and a few hundred satellites to LEO to enhance global bandwidth, starting this year.

Iridium, LeoSat, and SES O3B have all entered into partnerships with Thales Alenia Space, a leading designer of telecommunication and navigation satellites as well as orbital infrastructure. Thales’ resume also includes providing parts and services for the International Space Station, as well as playing major role in the development of the ATV cargo vessel, as part of the NASA/ESA Cygnus program.

In conjunction with Thales and Boeing, SES 03b plans to use its proposed constellation of 27 satellites to bridge the global digital divide. In the past, O3b was in the practice of providing cruise ships with wireless access. After merging with SES in 2016, they expanded their vision to include geosynchronous-Earth-oribit and MEO satellites. The company plans to have all its satellites operational by 2021.

Iridium is also partnering with Orbital ATK, the commercial aerospace company, to make their constellation happen. And whereas other companies are focused on providing enhanced bandwidth and access, Iridium’s main goal is to provide safety services for cockpit Wi-Fi. These services will be restricted to non-passenger flights for the time being, and will operate in the L and K_a bands.

And the there’s LeoSat’s plan to send up to 108 satellites to LEO which will be interconnected through laser links to provide what they describe as “an optical backbone in space about 1.5 times faster than terrestrial fiber backbones”. The first of these small, high-throughput satellites – which will deliver services in the K_a-band – is scheduled to launch in 2019.

Similarly, Telesat LEO hopes to create an internet satellite network to provide services that are comparable to fiber-optic internet connections. According to the company, their services will target “busy airports; military operations on land, sea and air; major shipping ports; large, remote communities; and other areas of concentrated demand.” The company plans to deploy two prototype satellites to LEO later this year, which were developed in conjunction with Airbus’ SSTL and Space Systems Loral.

With all the developments taking place these days, it does seem like the dream of a global internet (much like the Internet of Things (IoT) is fast becoming a reality. In the coming decades, we may look back at the late 20th and early 21st centuries the same way we look at the stone ages. Compared to a world where almost everyone has internet access and can download, upload, stream and surf, a world where only a few million people could do that will seem quite primitive!

Featured: Aviation Week, Popular Mechanics

January 5, 2018 by Matt Williams

The Gaia Mission Could Moonlight as a Gravitational Wave Detector

The ESA's Gaia mission is currently on a five-year mission to map the stars of the Milky Way. Gaia has found evidence for a galactic collision that occurred between 300 million and 900 million years ago. Image credit: ESA/ATG medialab; background: ESO/S. Brunier.

In February of 2016, scientists working for the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first-ever detection of gravitational waves. Since that time, multiple detections have taken place, thanks in large to part to improvements in instruments and greater levels of collaboration between observatories. Looking ahead, its possible that missions not designed for this purpose could also “moonlight” as gravitational wave detectors.

For example, the Gaia spacecraft – which is busy creating the most detailed 3D map of the Milky Way – could also be instrumental when it comes to gravitational wave research. That’s what a team of astronomers from the University of Cambridge recently claimed. According to their study, the Gaia satellite has the necessary sensitivity to study ultra-low frequency gravitational waves that are produced by supermassive black hole mergers.

The study, titled “Astrometric Search Method for Individually Resolvable Gravitational Wave Sources with Gaia“, recently appeared in the Physical Review Letters. Led by Christopher J. Moore, a theoretical physicist from the Center for Mathematical Sciences at the University of Cambridge, the team included members from Cambridge’s Institute of Astronomy, Cavendish Laboratory, and Kavli Institute for Cosmology.

To recap, gravitational waves (GWs) are ripples in space-time that are created by violent events, such as black hole mergers, collisions between neutron stars, and even the Big Bang. Originally predicted by Einstein’s Theory of General Relativity, observatories like LIGO and Advanced Virgo detect these waves by measuring the way space-time flexes and squeezes in response to GWs passing through Earth.

However, passing GWs would also cause the Earth to oscillate in its location with respect to the stars. As a result, an orbiting space telescope (such as Gaia), would be able to pick up on this by noting a temporary shift in the position of distant stars. Launched in 2013, the Gaia observatory has spent the past few years conducting high-precision observations of the positions of stars in our Galaxy (aka. astrometry).

In this respect, Gaia would look for small displacements in the massive field of stars it is monitoring to determine if gravitational waves have passed through the Earth’s neighborhood. To investigate whether or not Gaia was up to the task, Moore and his colleagues performed calculations to determine if the Gaia space telescope had the necessary sensitivity to detect ultra-low frequency GWs.

To this end, Moore and his colleagues simulated gravitational waves produced by a binary supermassive black hole – i.e. two SMBHs orbiting one another. What they found was that by compressing the data sets by a factor of more than 10⁶ (measuring 100,000 stars instead of a billion at a time), GWs could be recovered from Gaia data with an only 1% loss of sensitivity.

Figure showing a Gaia star field, with red and black lines indicating induced apparent motions of the stars within a hemisphere. Credit: Kavli Institute for Cosmology, Cambridge

This method would be similar to that used in Pulsar Timing Arrays, where a set of millisecond pulsars are examined to determine if gravitational waves modify the frequency of their pulses. However, in this case, stars are being monitored to see if they are oscillating with a characteristic pattern, rather than pulsing. By looking at a field of 100,000 stars at a time, researchers would be able to detect induced apparent motions (see figure above).

Because of this, the full release of Gaia data (scheduled for the early 2020s) is likely to be a major opportunity for those hunting for GW signals. As Moore explained in a APS Physics press release:

“Gaia will make measuring this effect a realistic prospect for the first time. Many factors contribute to the feasibility of the approach, including the precision and long duration of the astrometric measurements. Gaia will observe about a billion stars over 5–10 years, locating each one of them at least 80 times during that period. Observing so many stars is the major advance provided by Gaia.”

It is also interesting to note that the potential for GW detection was something that researchers recognized when Gaia was still being designed. One such individual was Sergei A. Klioner, a researcher from the Lorhrmann Observatory and the leader of the Gaia group at TU Dresden. As he indicated in his 2017 study, “Gaia-like astrometry and gravitational waves“, Gaia could detect GWs caused by merging SMBHs years after the event:

“It is clear that the most promising sources of gravitational waves for astrometric detection are supermassive binary black holes in the centers of galaxies… It is believed that binary supermassive black holes are a relatively common product of interaction and merging of galaxies in the typical course of their evolution. This sort of objects can give gravitational waves with both frequencies and amplitudes potentially within the reach of space astrometry. Moreover, the gravitational waves from those objects can often be considered to have virtually constant frequency and amplitude during the whole period of observations of several years.”

*Artist’s impression of two merging black holes, which has been theorized to be a source of gravitational waves. Credit: Bohn, Throwe, Hébert, Henriksson, Bunandar, Taylor, Scheel/SXS*

But of course, there’s no guarantees that sifting through the Gaia data will reveal additional GW signals. For one thing, Moore and his colleagues acknowledge that waves at these ultra-low frequencies could be too weak for even Gaia to detect. In addition, researchers will have to be able to distinguish between GWs and conflicting signals that result from changes in the spacecraft’s orientation – which is no easy challenge!

Still, there is hope that missions like Gaia will be able to reveal GWs that are not easily visible to ground-based interferometric detectors like LIGO and Advanced Virgo. Such detectors are subject to atmospheric effects (like refraction) which prevent them from seeing extremely low frequency waves – for instance, the primordial waves produced during the inflationary epoch of the Big Bang.

In this sense, gravitational wave research is not unlike exoplanet research and many other branches of astronomy. In order to find the hidden gems, observatories may need to take to space to eliminate atmospheric interference and increase their sensitivity. It is possible then that other space telescopes will be retooled for GW research, and that next-generation GW detectors will be mounted aboard spacecraft.

In the past few years, scientists have gone from making the first detection of gravitational waves to developing new and better ways to detecting them. At this rate, it won’t be long before astronomers and cosmologists are able to include gravitational waves into our cosmological models. In other words, they will be able to show what influence these waves played in the history and evolution of the Universe.

Further Reading: Kavli Institute for Cosmology, APS Physics, Physical Review Letters