Posted on by Shannon Hall

Novel Strategy May Help Target Extraterrestrial Intelligent Life

Photo: Mike Agliolo/Corbis

Discovering life beyond Earth might just be the holy grail of science. And even though we have yet to find evidence for little green men or blobs of bacteria, astronomers continue to search for elusive signs of life.

A novel strategy may help astronomers better target extraterrestrial intelligent life. Dr. Michael Gillon, of the University of Liege in Belgium, proposes an approach that would monitor the regions of nearby stars to search for interstellar communication devices.

The most common method in the search for extraterrestrial intelligence (abbreviated as SETI) is the use of giant radio dishes to scan the stars, listening for possible faint signals coming from distant civilizations.

While the SETI institute has been hard at work since 1959 we haven’t chanced upon a signal yet. But that doesn’t mean we’re alone or that we should stop looking.

Even without a confirmed extraterrestrial signal, most astronomers would argue that recent discoveries have strongly reinforced the hypothesis that extraterrestrial life may just be abundant in the Universe. With the help of the Kepler Space Telescope we have learned that planets are plentiful throughout the Milky Way. With most stars harboring at least one planet, it’s conceivable that a few of those planets will have the right conditions for life.

So why haven’t we detected extraterrestrial intelligent life? Why do we have this glaring Fermi Paradox — the apparent contradiction between the high probability of extraterrestrial civilizations’ existence and the lack of contact with such civilizations?

One hypotheses to explain the famous Fermi Paradox is that self-replicating probes could have explored the whole Galaxy, including our Solar System, but we just haven’t detected them yet. A self-replicating probe is one sent to a nearby planetary system where it would mine raw materials to create a replica of itself that would then head towards other nearby systems, continuing to replicate itself along the way.

While our own technological civilization is less than two hundred years old, we have already sent robotic probes to a large number of bodies in our Solar System and beyond. Our furthest-reaching probe, Voyager 1, just made it to interstellar space. But it took it over 40 years.

“We are still far from being able to build an actual self-replicating interstellar spaceship, but only because our technology is not mature enough, and not because of an obvious physical limitation,” Dr. Gillon told Universe Today.

While we cannot currently send self-replicating probes to the nearest stars in a reasonable amount of time, nothing excludes this as a reachable future project, or a project already completed by extraterrestrial intelligent life.

This study further proposes that probes from neighboring stellar systems could use the stars they orbit as gravitational lenses to communicate efficiently with each other.

The coordination of probes to explore the Galaxy would be very inefficient unless they had the ability to directly communicate with one another. The vastness and structure of the Milky Way makes this seemingly impossible. By the time a signal reached a very distant star it would be highly diluted.

However, any star is massive enough to bend and amplify light. This process, gravitational lensing, is extremely powerful. “It means that the Sun (and any other star) is an antenna much more powerful than we could ever build,” says Dr. Gillon.

Based on this method, interstellar communication devices will exist along the line that connects one star to another. We now know exactly where to look, and even where to send messages.

Could this novel idea provide a new mission for SETI?

“A negative result wouldn’t tell us very much,” explains Dr. Gillon. “But a positive result would represent one of the most important discoveries of all time.”

The paper has been accepted for publication in Acta Astronautica and is available for download here.

Posted on by Shannon Hall

Earth and Climate: Two Scenarios of Our Planet in 2100 AD

The Earth at night. What will it look like 100 years from now? Image credit: NASA-NOAA

The Earth is warming up.

Ocean temperatures are rising. Arctic sea ice is melting. Atmospheric carbon dioxide levels are growing. The oceans are becoming more acidic. The weather is already more extreme.

With the release of the fifth Assessment Report by the Intergovernmental Panel on Climate Change – a panel of more than 2,500 experts, more commonly known as the IPCC –  it’s clear that climate change is very real. But it’s especially clear that we are the cause. If we don’t act now by taking vigorous action to reduce emissions the results will be catastrophic.

Toward the end of this 900-page report, the IPCC looked toward our future, focusing on the climate after the year 2100. Here, Universe Today, explores two extreme scenarios for the Earth by 2100.

1.) Embracing the Challenges of Climate Change

The conclusions reached by climate scientists at the end of the 21st Century were undeniable. We embraced climate change by investing heavily in renewable energies. Both large-scale companies and individuals bought energy drawn from the sunlight, wind, and geothermal heat.

Homes across the world became more sustainable. Their total square feet shrunk, as home owners learned to live with less. It was not uncommon to dress a roof with plants or solar panels. Even the layout of homes changed. They rested partially underground, taking advantage of geothermal heat, and faced South (in the case of the Northern hemisphere) to take advantage of the warm sunlight.

We also embraced geoengineering technologies.  We added artificial clouds to our atmosphere, which reflected sunlight, and built towers to collect greenhouse gas emissions. The gases are now trapped deep underground. Our goal was not only to slow the process of climate change, but to stop it, and quite possibly reverse it.

We now eat far less meat than we did in the early 21st Century to cut the emissions generated from livestock farming. Pastures have been replaced with booming forests – helping to absorb CO2. We also eat more locally.

The world followed in China’s footsteps and restricted couples to a certain number of children, reducing our overall population.

We live in small compact cities where we drive hybrid cars and take public transport to work. Carbon offsets must be purchased when taking long trips. Most families vacation in their own backyard – exploring all that nature has to offer in the nearby vicinity.

We viewed climate change as an exciting opportunity to embrace the needs of our environment. We now live much simpler lives and the census shows that our overall intelligence and happiness is much higher than it was a century ago.

2.) The Point of No Return

We simply didn’t want to face the facts. We live in a global economy with a population that has increased significantly over the last century. Most of our energy still comes from fossil fuels. We never invested in renewable energies.

We measure our happiness based on the cars we drive, the number of material possessions we can cram into our large homes, and how often we travel the globe.

The world is, on average, 9 degrees warmer. The entire arctic has melted. Ocean levels have risen by over a meter – flooding coastal communities across the world. Millions have been left homeless.

Our weather is extreme. Hurricanes, tornadoes, fires, floods, draughts, and earthquakes kill hundreds of thousands per year.  Climate change has devastated food production and water supplies.

Air quality is much poorer across the world. Due to haze, it is perfectly safe to look at the sun directly. We can only see a third of the stars visible a century ago.

We have triggered various tipping points. The thawing of permafrost released further CO2 and methane. Large areas of the planet are becoming uninhabitable. Our efforts are working toward damage control only. We fear that it may be too late.

Climate change is still in our hands, but we have to act now.

The fifth Assessment Report by the IPCC may be found here. Emphasis in this article may be found in the long term climate change section, as well as descriptions published by the IPCC in 2000.

Posted on by Shannon Hall

Detecting the Magnetic Fields of Exoplanets May Help Determine Habitability

An artist's conception of two magnetic fields interacting in a bow shock. Image credit: NASA

Astronomers may soon be able to observe the shockwaves between the magnetic fields of exoplanets and the flow of particles from the stars they orbit.

Magnetic fields are crucial to a planet’s (and as it turns out a moon’s) habitability. They act as protective bubbles, preventing harmful space radiation from stripping away the object’s atmosphere entirely and even reaching the surface.

An extended magnetic field – known as a planetary magnetosphere – is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge. Within our own Solar System, Jupiter’s magnetosphere extends to distances up to 50 times the size of the planet itself, nearly reaching Saturn’s orbit.

When the wind of high-energy particles from the star hits the planetary magnetosphere, it interacts in a bow shock that diverts the wind and compresses the magnetosphere.

Recently a team of astronomers, led by PhD student Joe Llama of the University of St. Andrews, Scotland, have worked out how we might observe planetary magnetospheres and stellar winds via their bow shocks.

Llama took a careful look at the planet HD 189733b, located 63 light years away toward the constellation Vulpecula. From the Earth, the planet is seen to transit its host star every 2.2 days, causing a dip in the overall light from the system.

As a bright star, HD 189733b has been studied extensively by astronomers.  Data collected in July 2008 by the Canada-France-Hawaii telescope mapped the star’s magnetic field. While the magnetic field varied, it was on average 30 times greater than that of our Sun – meaning that the stellar wind is much higher than the solar wind.

This allowed the team to carry out extensive simulations of the stellar wind around HD 189733b – characterizing the bow shock created as the planet’s magnetosphere passes through the stellar wind.  With this information they were able to simulate the light curves that would result from the planet and the bow shock orbiting the star.

The bow shock leads the planet – causing the light to drop a little earlier than expected.  The amount of light blocked by the bow shock, however, will change as the planet moves through a variable stellar wind. If the stellar wind is particularly strong, the resulting bow shock will be strong, and the transit depth will be greater. If the stellar wind is weak, the resulting bow shock will be weak, and the transit depth will be less.

The video below shows the light curve of a bow shock and exoplanet.

“We found that the shockwave between the stellar and planetary magnetic fields will change drastically as activity on the star varies,” Llama told Universe Today. “As the planet passes through very dense regions of the stellar wind, so the shock will become denser, the material in it will block more light and therefore cause a larger dip in the transit making it more detectable.”

While there were no transit observations for this study, this theoretical outlook demonstrates that it will be possible to detect the bow shock, and therefore the magnetic field, of a distant exoplanet. Dr. Llama comments: “This will help us to better identify potentially habitable worlds.”

The paper has been accepted for publication in Monthly Notices of  The Royal Astronomical Society and is available for download here.

 

Posted on by Shannon Hall

This Planetary Nebula Comes With a Twist

From the Cat’s Eye to the Eskimo, planetary nebulae are arguably among the most dazzling objects in the Universe. These misnamed stellar remnants are created when the outer layers of a dying star blows off and expands into space. However, they can look radically different from one another, revealing complicated histories and structures.

But recently, astronomers have argued that some of the most exotic shapes are the result of not one, but two stars at the center. It is the interaction between the progenitor star and a binary companion that shapes the resulting planetary nebula.

The archetypal planetary nebula is spherical. Most planetary nebulae, however, have been shown to be non-spherical, complex structures.

“LoTr 1 is one such planetary nebula, but with a twist,” Amy Tyndall – a graduate student at the University of Manchester and lead author on the study – told Universe Today. It has not one star at its center but two. The binary central star system consists of a faint, hot white dwarf and a cool companion – a rapidly rotating giant.

LoTr 1 with a binary central star system and two slightly elongated shells, with ages of 17 and 35 thousand years.
LoTr 1 with a binary central star system and two slightly elongated shells, with ages of 17 and 35 thousand years. Credit: Tyndal et al.

LoTr 1 was first discovered by astronomers using the 1.2 meter telescope at the Royal Observatory in Edinburgh, Scotland. At the time it seemed that LoTr 1 was similar to a particular group of 4 planetary nebulae (Abell 35, Abell 70, WeBo 1 and LoTr 5), all of which had a central binary star system.

Another common factor amongst this particular group is that in most cases the companion star seemed to be a barium star – a cool giant that shows relatively large amounts of barium. Before the planetary nebula forms, the progenitor star dredges up an excess amount of Barium on its surface. It then releases a Barium-enriched stellar wind, which falls on its companion star.

“After the stellar envelope is ejected to form the surrounding nebula, the giant star evolves into a white dwarf, while the contaminated star retains the barium from the wind as it continues to evolve to form a Barium star,” explains Tyndall.

Tyndall and her collaborates set out to see if the companion star within LoTr 1 was in fact a Barium star. They acquired data from telescopes in both Chile and Australia and compared their results to the two other elusive planetary nebulae in the group: Abell 70 and WeBo 1.

“If barium is indeed present, it would be a good step further towards our understanding of how mass is transferred between stars in a binary system, and how that subsequently affects the formation and morphology of planetary nebulae,” says Tyndall.

While the results show that LoTr 1 does consist of binary star system, the companion star is not a Barium star. But a null result is still a result. “LoTr 1 remains an interesting object to us as it shows that we still have huge gaps in our knowledge as to how these stunning objects form,” Tyndall told Universe Today.

Without the presence of Barium, it would appear at first that little mass was transferred to the companion star. However, the companion star is rotating rapidly, which is a direct consequence of mass transfer. The most plausible explanation is that the mass was transferred before the barium could be dredged up to the stellar surface.

If the stellar evolution was cut short this way then there will be detectable evidence in the properties of the white dwarf. The next step will be to take another look at this odd planetary nebula in hopes of better understanding the complexities of this system.

The paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is available for download here.

Posted on by Shannon Hall

Magnetic Fields are Crucial to Exomoon Habitability

Artist's conception of an Earth-like exomoon orbiting a gaseous planet. Image credit: Avatar, 20th Century Fox

Astronomers believe that hidden deep within the wealth of data collected by NASA’s Kepler mission are minuscule signatures confirming the presence of exomoons. With such a promising discovery on the horizon, researchers are beginning to address the factors that may deem these alien moons habitable.

A new study led by Dr. René Heller from McMaster University in Canada and Dr. Jorge Zuluaga from the University of Antioquia in Colombia takes a theoretical look at habitability – exploring the key components that may make exomoons livable.  While stellar and planetary heating play a large role, it’s quickly becoming clear that the magnetic environments of exomoons may be even more critical.

An exoplanet’s habitability is first and foremost based on the circumstellar habitable zone – the temperature band around a star in which water may exist in its liquid state. Exomoons, however, have an additional set of constraints that affect their habitability. In a set of recent papers, Dr. Heller and Dr. Rory Barnes (from the University of Washington) defined a “circumplanetary habitable edge,” which is roughly analogous to the circumstellar habitable zone.

Here the question of habitability is based on the relationship between the exomoon and its host planet. The additional energy source from the planet’s reflected starlight, the planet’s thermal emission, and tidal heating in the moon may create a runaway greenhouse effect, rendering the exomoon uninhabitable.

One look at Io – Jupiter’s closest Galilean satellite – shows the drastic effects a nearby planet may have on its moon.  The strong gravitational pull of Jupiter distorts Io into an ellipsoid, whose orbit around the giant planet is eccentric due to perturbations from the other Galilean moons. As the orbital distance between Jupiter and Io varies on an eccentric orbit, Io’s ellipsoidal shape oscillates, which generates enormous tidal friction. This effect has led to over 400 active volcanic regions.

Note that this is an edge, not a zone.  It defines only an innermost habitable orbit, inside which a moon would become uninhabitable. The exomoon must exist outside this edge in order to avoid intense planetary illumination or tidal heating.  Exomoons situated in distant orbits, well outside the circumplanetary habitable edge, have a chance at sustaining life.

But the question of habitability doesn’t end here. Harmful space radiation can cause the atmosphere of a terrestrial world to be stripped off. Planets and moons rely heavily on magnetic fields to act as protective bubbles, preventing harmful space radiation from depleting their atmospheres.

With this in mind, Heller and Zuluaga set out to understand the evolution of magnetic fields of extrasolar giants, which are thought to affect their moons. It’s unlikely that small, Mars-sized exomoons will produce their own magnetic fields. Instead, they may have to rely on an extended magnetic field from their host planets.

This planetary magnetosphere is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge, protecting moons in very distant orbits.  Within our own Solar System Jupiter’s magnetosphere ends at distances up to 50 times the size of the planet itself.

Heller and Zuluaga computed the evolution of the extent of a planetary magnetosphere.  “Essentially, as the pressure of the stellar wind decreases over time, the planetary magnetic shield expands,” Dr. Heller told Universe Today. “In other words, the planetary magnetosphere widens over time.”

Evolution of the host planets magnetosphere for a
Evolution of the host planets magnetosphere (represented by the blue line) for Neptune-, Saturn-, and Jupiter-like planets. All increase over time by a varying amount.

The team applied these two models to three scenarios: Mars-sized moons orbiting Neptune-, Saturn-, and Jupiter-like planets. These three systems were always located in the center of the circumstellar habitable zone of a 0.7 solar-mass star. Here are the take-home messages:

1.) Mars-like exomoons beyond 20 planetary radii around any of the three host planets act like free planets around a star. They are well outside the habitable edge, experiencing no significant tidal heating or illumination. While their extreme distance is promising, they will never be enveloped within their host planet’s magnetosphere and are therefore unlikely to harbor life.

2.) Mars-like exomoons between 5 and 20 planetary radii face a range of possibilities. “Intriguingly, formation theory and observations of moons in the Solar System tell us that this is the range in which we should expect most exomoons to reside,” explains Dr. Heller.

For an exomoon beyond the habitable edge of a Neptune-like planet it may take more than the age of the Earth, that is, 4.6 billion years to become embedded within its host planet’s magnetosphere. For a Saturn-like planet it may take even longer, but for a Jupiter-like planet it will take less than 4.3 billion years.

3.) Mars-like exomoons inside 5 planetary radii are enveloped within the planetary magnetosphere early on but not habitable as they orbit within the planet’s habitable edge.

In order for an exomoon to be habitable it must exist well outside the habitable edge, safe from stellar and planetary illumination as well as tidal heating. But at the same time it must also exist near enough to its host planet to be embedded within the planet’s magnetosphere. The question of habitability depends on a delicate balance.

Dr. Zuluaga stressed that “one of the key consequences of this initial work is that although magnetic fields have been recognized as important factors determining the habitability of terrestrial planets across the Universe, including the Earth, Mars, and Venus, in the case of moons, the magnetic environment could be even more critical at defining the capacity of those worlds to harbor life.”

The paper has been accepted for publication in the Astrophysical Journal Letters and is available for download here.

Posted on by Shannon Hall

New Molecules Detected in Io’s Atmosphere

An image of Io taken by the automated spacecraft: Galileo. Image Credit: NASA

Io – Jupiter’s innermost Galilean moon – is the most geologically active body in the Solar System. With over 400 active volcanic regions, plumes of sulfur can climb as high as 300 miles above the surface.  It is dotted with more than 100 mountains, some of which are taller than Mount Everest. In between the volcanoes and mountains there are extensive lava flows and floodplains of liquid rock.

Intense volcanic activity leads to a thin atmosphere consisting mainly of sulfur dioxide (SO2), with minor species including sulfur monoxide (SO), sodium chloride (NaCl), and atomic sulfur and oxygen. Despite Io’s close proximity to the Earth the composition of its atmosphere remains poorly constrained. Models predict a variety of other molecules that should be present but have not been observed yet.

Recently a team of astronomers from institutions across the United States, France, and Sweden, set out to better constrain Io’s atmosphere. They detected the second-most abundant isotope of sulfur (34-S) and tentatively detected potassium chloride (KCl). The latter is produced in volcanic plumes – suggesting that these plumes continuously contribute to Io’s atmosphere.

Expected yet undetected molecular species include potassium chloride (KCl), silicone monoxide (SiO), disulfur monoxide (S2O), and various isotopes of sulfur. Most of these elements emit in radio wavelengths.

“Depending on their geometry, some molecules emit at well known frequencies when they change rotational state,” Dr. Arielle Moullet, lead author on the study, told Universe Today. “These spectral features are called rotational lines and show up in the (sub)millimeter spectral range.”

These observations were therefore obtained at the Atacama Pathfinder Experiment (APEX) antenna – a radio telescope located 16,700 feet above sea level in northern Chile. The main dish has a diameter of 12 meters, and is a prototype antenna for the Atacama Large Millimeter Array (ALMA).

The Atacama Pathfinder (APEX) antenna. Image Credit: ESO
The Atacama Pathfinder (APEX) antenna. Image Credit: ESO

Following 16.5 hours of total observation time and months of data reduction and analysis, Moullet et al. made a tentative detection of potassium chloride (KCl). Io’s volcanic ejecta produce a large plasma torus around Jupiter, which inlcudes many molecular species including potassium.  This detection is therefore considered the “missing link” between Io and this plasma torus.

The team also made the first detection of one of Sulfur’s isotopes known as 34-S. Sulfur has 25 known isotopes – variants of sulfur that still have 16 protons but differ in their number of neutrons. 34-S is the second most abundant isotope with 18 neutrons.

Previously, the first-most abundant isotope of sulfur, 32-S with 16 neutrons, had been detected. Surprisingly the ratio between the two (34/32 S) is twice as high as the solar system reference, suggesting that there is an abundance of 34-S. A fraction this high has only been reported before in a distant quasar – an early galaxy consisting of an intensely luminous core powered by a huge black hole.

“This result tells us that there probably is some fractionation process that we haven’t yet identified, which is happening either in the magma, at the surface, or in the atmosphere itself,” explains Dr. Moullet.  Something somewhere is producing an unexplained abundance of this isotope.

Other expected yet undetected molecules including silicone monoxide and disulfur monoxide remain undetected. It is possible that these molecules are simply not present, but more likely that the observations are not sensitive enough to detect them.

“To perform a deeper spectral search with a better sensitivity, our group has been awarded observation time with the Atacama Large Millimeter Array, a cutting edge interferometric facility in Chile, which will eventually include more than fifty 12-meter wide dishes,” explains Dr. Moullet.  “We are in the process of analyzing our first dataset obtained with sixteen antennas, which is already much more sensitive than the APEX data.”

While Io is certainly an extreme example, it will likely help us characterize volcanism in general – providing a better understanding of volcanism here on Earth as well as outside the Solar System.

The paper has been accepted for publication in The Astrophysical Journal and is available for download here.

Posted on by Shannon Hall

Planet Evaporates Due to Stellar Flare

An artist's conception of a disintegrating planet - creating a trail of dust - around its rocky star.

Solar flares – huge eruptions of charged particles from the Sun – present little threat to Earth. On a few rare occasions these particles may disrupt our communications systems and cause radio blackouts. But they tend to be more aesthetically pleasing than harmful. It’s certainly a sight to be seen as these energetic particles collide with our atmosphere, resulting in a cascade of colorful lights – the aurora borealis.

Fortunately our planet provides the protection necessary from such harmful space radiation. But not all planets are quite so lucky. Take for instance Kepler’s latest object of interest: KIC 12557548b, a super Mercury-size planet candidate. Astronomers have recently found that due to this star’s activity – producing massive stellar flares – the planet itself is evaporating.

Only last year, four different sources published evidence that this rocky planet was disintegrating. Thanks to Kepler, it quickly became clear that the total amount of light from KIC 12557548 as a function of time – the light curve of the system – dropped every 15.7 hours as a planet orbited it. But the amount of light blocked due to the transiting planet varied from 0.2% to more than 1.2%.

The amount of light blocked is dependent on the size of the planet. A Jupiter-size planet will block more light than a Mercury-size planet.  The variations here suggest a range for the size of the planet: from a super Mercury-sized planet to a Jupiter-sized planet.

But this wasn’t the planet’s only enigma. It also has an asymmetric light curve. The total light from the star drops steadily as the planet begins its transit, plateaus as the planet fully covers the disk of the star, and then increases as the planet ends its transit.  But the rate at which the light drops is much faster than the rate at which it increases.  It takes longer for the light curve to return to its original brightness, hinting at a tail of debris that trails the planet, continuing to block light.

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The light curves of KIC 12557548b. The left-hand plot represents deep transits, whereas the right-hand plot represents more shallow transits.  Both plots show a clear asymmetry. Source: Brogi et al. 2012

It appears that the planet is evaporating – emitting small particles of dust into orbit, which then trails behind it. The varying transit depth reflects the amount of dust currently evaporating.

Recently a team from the University of Tokyo analyzed the system in more detail, attempting to explain why this tiny planet is evaporating. “We found that the transit depth negatively correlates with the modulation of the stellar flux,” Dr. Kawahara, lead author on the study, told Universe Today. “The dust amount increases when the planet is located in front of the star spots.”

The transit depth does not vary randomly, but every 22.83 days. This coincides with the modulation of the stellar flux, or simply the stellar rotation period.  Star spots may be indirectly detected by a star’s noticeable decrease in stellar flux.  Because these star spots are large (much larger than sunspots) they last for long periods of time, and may be used to deduce the star’s rotation period.

Kawahara et al. found that the transit depth periodically varies with the stellar rotation rate – finding a correlation between stellar activity and the rate at which the planet is evaporating.

“Energy from the star spots increases the amount of dust and atmosphere from the planet,” explains Dr. Kawahara. The extreme heat and wind is enough to speed up the motions of the dust molecules; making them fast enough to escape the planet’s gravitational pull.

Future spectroscopic studies may search for molecules in the evaporating atmosphere of KIC 12557548b.  But Dr. Kawahara remarks that due to the planet’s faintness it is unlikely. His best hope is that future studies may instead find a similar object closer to us, that may be more easy to study.

The finding is published in The Astrophysical Journal Letters and is available for download here.

Posted on by Shannon Hall

New Exoplanet Research: Magnetic Fields Significantly Affect Hot Jupiter Atmospheres

Click here.

Determining weather patterns in exoplanet atmospheres – hundreds to thousands of light years away – is extremely difficult. However, given that it may be one of our best ways to truly characterize these alien words, it’s a challenge astronomers have accepted willingly.

Most models have a very simple foundation, necessarily eliminating the complex physics that is difficult to incorporate and analyze.  Recently, a team led by Dr. Konstantin Batygin of Harvard University, added one more parameter to their models, drastically changing their results.

The punch line is this: the inclusion of magnetic fields significantly changes, and actually simplifies, the atmospheric circulation of hot Jupiters.

Hot Jupiters orbit dangerously close to their host stars, roasting in stellar radiation. But they are also tidally locked to their host stars – one hemisphere continually faces the star, while one continuously faces away – creating a permanent dayside and a permanent nightside.

One would expect the temperature gradient between the dayside and the nightside to be very high. However, various weather patterns play a role in strongly decreasing this temperature gradient. As an example, we now know that clouds may significantly decrease the temperature of the dayside.

Dr. Batygin’s team analyzed magnetic effects within atmospheric circulation. “The case of hot Jupiters is quite peculiar,” she told Universe Today. “The atmospheres of hot Jupiters have temperatures that reach up to 2000 Kelvin, which is hot enough to ionize trace Alkali metals such as potassium and sodium.  So the air on hot Jupiters is actually a weakly conducting plasma.”

Once the alkali metals have been ionized – stripped of their electrons – the upper atmosphere contains all of those charged particles and becomes a plasma. It is then electrically conductive and magnetic effects must be taken into account.

While the underlying physics is pretty complex (with nearly 40 multi-lined equations in the paper alone), the introduction of magnetic effects actually simplified the model’s outcome.

In the absence of magnetic fields, the upper and lower atmospheres feature two distinct patterns of circulation. The upper atmosphere consists of winds blowing away from the dayside in all directions. And the lower atmosphere consists of zonal flows – the bands of color on Jupiter.  The zonal flows move parallel to lines of latitude in an east-west fashion. Each moves in a different direction than the one above and below it.

“Upon introducing magnetic fields, fancy dayside-to-nightside flows are quenched and the entire atmosphere circulates in an exclusively east-west fashion,” explains Dr. Batygin. The upper atmosphere resembles the lower atmosphere – zonal flows dominate.

Throughout these models, Dr. Batygin et al. assumed a magnetic field aligned with the rotation axis of the planet. Future work will include a closer look at the effect of a more complicated geometry. The team also intends to extend these results to hotter atmospheres, where magnetic fields will slow the rate of these zonal flows. According to Dr. Batygin, “this has potentially observable consequences and we hope to elucidate them in the future.”

These results will be published in the astrophysical journal (preprint available here).

Posted on by Shannon Hall

When do Black Holes Become Active? The Case of the Strangely-Shaped Galaxy Mrk 273

Mrk 273 as seen by the Hubble Space Telescope.

The Hubble image above shows a strange galaxy, known as Mrk 273.  The odd shape – including the infrared bright center and the long tail extending into space for 130 thousand light-years – is strongly indicative of a merger between galaxies.

Near-infrared observations have revealed a nucleus with multiple components, but for years the details of such a sight have remained obscured by dust. With further data from the Keck Telescope, based in Hawaii, astronomers have verified that this object is the result of a merger between galaxies, with the infrared bright center consisting of two active galactic nuclei – intensely luminous cores powered by supermassive black holes.

At the center of every single galaxy is a supermassive black hole. While the name sounds exciting, our supermassive black hole, Sgr A* is pretty quiescent.  But at the center of every early galaxy looms the opposite: an active galactic nuclei (AGN for short). There are plenty of AGN in the nearby Universe as well, but the question stands: how and when do these black holes become active?

In order to find the answer astronomers are looking at merging galaxies. When two galaxies collide, the supermassive black holes fall toward the center of the merged galaxy, resulting in a binary black hole system. At this stage they remain quiescent black holes, but are likely to become active soon.

“The accretion of material onto a quiescent black hole at the center of a galaxy will enable it to grow in size, leading to the event where the nucleus is “turned on” and becomes active,” Dr. Vivian U, lead author on the study, told Universe Today. “Since galaxy interaction provides means for gaseous material in the progenitor galaxies to lose angular momentum and funnels toward the center of the system, it is thought to play a role in triggering AGN.  However, it has been difficult to pinpoint exactly how and when in a merging system this triggering occurs.”

While it has been known that an AGN can “turn on” before the final coalescence of the two black holes, it is unknown as to when this will happen. Quite a few systems do not host dual AGN.  For those that do, we do not know whether synchronous ignition occurs or not.

Mrk 273 provides a powerful example to study. The team used near-infrared instruments on the Keck Telescope in order to probe past the dust.  Adaptive optics also removed the blurring affects caused by the Earth’s atmosphere, allowing for a much cleaner image – matching the Hubble Space Telescope, from the ground.

“The punch line is that Mrk 273, an advanced late-stage galaxy merger system, hosts two nuclei from the progenitor galaxies that have yet to fully coalesce,” explains Dr. U. The presence of two supermassive black holes can be easily discerned from the rapidly rotating gas disks that surround the two nuclei.

“Both nuclei have already been turned on as evidenced by collimated outflows (a typical AGN signature) that we observe” Dr. U told me. Such a high amount of energy released from both supermassive black holes suggests that Mrk 273 is a dual AGN system. These exciting results mark a crucial step in understanding how galaxy mergers may “turn on” a supermassive black hole.

The team has collected near-infrared data for a large sample of galaxy mergers at different merging states.  With the new data set, Dr. U aims “to understand how the nature of the nuclear star formation and AGN activity may change as a galaxy system progresses through the interaction.”

The results will be published in the Astrophysical Journal (preprint available here).

 

Posted on by Shannon Hall

Newly Discovered Fast Radio Bursts May be Colliding Neutron Stars

An artist's conception of two neutron stars, moments before they collide. Image Credit: NASA

The Universe is sizzling with undiscovered phenomena. Only last month astronomers heard four unexpected bumps in the night. These Fast Radio Bursts released torrents of energy, each occurred only once, and lasted a few thousandths of a second. Their origin has since mystified astronomers.

Dismissing my first guess, which includes a feverish Jodie Foster verifying the existence of extraterrestrial life, astronomers have found a more likely answer. Two neutron stars collide, but before doing so produce a quick burst of radio emission, which we later observe as a Fast Radio Burst.

Our first hint? These Fast Radio Bursts are extra-galactic in origin.  The exact distance is quantifiable from a “dispersion measure – the frequency dependent time delay of the radio signal,” Dr. Tomonori Totani, lead author on the paper, told Universe Today. “This is proportional to the number of electrons along the line of sight.”

For all bursts, the short-wavelength component arrived at the telescope a fraction of a second before the longer wavelengths.  This is due to an effect known as interstellar dispersion: through any medium, longer-wavelength light moves slightly slower than short-wavelength light.

Light from extra-galactic objects will have to travel through intergalactic space, which is teeming with electrons in clouds of cold plasma. The farther the light travels, the more electrons it will have to travel through, and the greater the time delay between arriving wavelength components. By the time light reaches the Earth, it has been dispersed, and the amount of dispersion is directly correlated with distance.

These Fast Radio Bursts are likely to have originated anywhere from 5 to 10 billion light years away.

While the exact source of these Fast Radio Bursts has been highly debated, a recent hypothesis concludes that they are the result of merging neutron stars in the distant Universe.

In the final milliseconds before merging, the rotation periods of the two neutron stars synchronize – they become tidally locked to one another as the Moon is tidally locked to the Earth. At this point their magnetic fields also synchronize. Energetic charged particles spiral along the strong magnetic field lines and emit a beam of radio synchrotron emission.

Known neutron star magnetic field strengths are consistent with the radio flux observed in these Fast Radio Bursts.  The emission then ceases in a few milliseconds when the two neutron stars have collided, which explains the short duration of these Fast Radio Bursts.

Not only does this mechanism describe both the high energy and the time duration of these bursts, but they’re inferred occurrence rate as well. It’s likely that 100,000 Fast Radio Bursts occur each day. This matches the likely neutron star merger rate.

Merging neutrons stars will also create gravitational waves – ripples in the curvature of spacetime that propagate away from the event. Dr. Totani emphasized that the next step will be to perform a correlated search of gravitational waves and Fast Radio Bursts. Such a fast rate estimate is certainly good news for scientists hoping to detect gravitational waves in the nearby future.

The Universe is bursting with energy – literally – every 10 seconds, and until recently we simply had no idea. This recently discovered phenomenon is likely to be the center of a new active area of research. And I have no doubt that it will lead to exciting discoveries that just may break trends and burst into new territories.

The discovery paper may be found here, while the paper analyzing neutron stars as a likely source may be found here.