The primary mission of the twin STEREO probes is to explore the 3-dimensional makeup of our Sun. Each craft carries a variety of instruments. One of them, the Heliospheric Imager (HI), doesn’t look directly at the Sun, but rather, explores a wide field near the Sun in order to explore the physics of coronal mass ejections (CMEs), in particular, ones aimed at the Earth. But while not focusing on solar ejections, the HI is free to make many other observations, including its first detection of an extrasolar planet.
As the Heliospheric Imager stares at the space between the Earth and Sun, it has made many novel observations. The device first opened its shutters in 2006 the instrument has observed the interaction of CMEs with the atmosphere of Venus, the stripping of a tail of a comet by a CME, atomic iron in a comet’s tail, and “the very faint optical emission associated with so-called Corotating Interaction Regions (CIRs) in interplanetary space, where fast-flowing Solar wind catches up with slower wind regions.”
The spacecraft allows for long periods of time to stare at patches of sky as the satellites precede and follow Earth in its orbit. The spacecraft is able to take pictures roughly every 40 minutes for almost 20 days in a row giving excellent coverage. As a result, the images taken have the potential to be used for detailed survey studies. Such information is useful for conducting variable star studies and a recent summary of findings from the mission reported the detection of 263 eclipsing variable stars, 122 of which were not previously classified as such.
Another type of variable star observed by the STEREO HI, was the cataclysmic sort, in particular, V 471 Tau. This red giant/white dwarf binary in the Hyades star cluster is a strong source of interest for stellar astrophysicists because the system is suspected to be a strong candidate for a type Ia supernova as the red giant dumps mass onto its high mass, white dwarf companion. The star system is extremely erratic in its light output and observations could help astronomers understand how such systems evolve.
Although planetary hunting is at the very edge of the capabilities of the HI’s limitations, eclipses caused by planet sized objects are feasible for many of the brighter stars in the field of view as dim as approximately 8th magnitude. Around one star, HD 213597, the STEREO team reported the detection of an object that seems too small to be a star based on the light curve alone. However, follow up studies will be necessary to pin down the object’s mass more accurately.
Artist's concept of buckyballs and polycyclic aromatic hydrocarbons around an R Coronae Borealis star rich in hydrogen. Credit: MultiMedia Service (IAC)
[/caption]When I first heard about buckyballs a couple of decades ago, I had nothing but the deepest respect for anyone who understood abstract ideas like string theory and branes. After all, how often were you likely to discuss Buckminster fullerenes with a contemporary while standing in the laundry detergent aisle of your local grocery store? The very concept of “magnetic” carbon was new and exciting! It was known to exist in small quantities in nature – produced by lightning and fire – but the real kicker was born solely in a laboratory. Buckyballs have been found on Earth and in meteorites, and now in space, and can act as “cages” to capture other atoms and molecules. Some theories suggest that the buckyballs may have carried to the Earth substances that make life possible.
According to the McDonald Observatory press release: Observations made with NASA’s Spitzer Space Telescope have provided surprises concerning the presence of buckminsterfullerenes, or “buckyballs,” the largest known molecules in space. A study of R Coronae Borealis stars by David L. Lambert, Director of The University of Texas at Austin’s McDonald Observatory, and colleagues shows that buckyballs are more common in space than previously thought. The research will appear in the March 10 issue of The Astrophysical Journal. The team found that “buckyballs do not occur in very rare hydrogen-poor environments as previously thought, but in commonly found hydrogen-rich environments and, therefore, are more common in space than previously believed,” Lambert says.
Buckyballs are made of 60 carbon atoms arranged in shape similar to a soccer ball, with patterns of alternating hexagons and pentagons. Their structure is reminiscent of Buckminster Fuller’s geodesic domes, for which they are named. These molecules are very stable and difficult to destroy. Richard Curl, Harold Kroto, and Richard Smalley won the 1996 Nobel Prize in chemistry for synthesizing buckyballs in a laboratory. The consensus based on lab experiments has been that buckyballs do not form in space environments that have hydrogen, because the hydrogen would inhibit their formation. Instead, the idea has been that stars with very little hydrogen but rich in carbon — such as the so-called “R Coronae Borealis stars” — provide an ideal environment for their formation in space.
Lambert, along with N. Kameswara Rao of Indian Institute of Astrophysics and Domingo Anibal García-Hernández of the Instituto de Astrofisica de Canarias, put these theories to the test. They used Spitzer Space Telescope to take infrared spectra of R Coronae Borealis stars to look for buckyballs in their chemical make-up. They found these molecules do not occur in those R Coronae Borealis stars with little or no hydrogen, an observation contrary to expectation. The group also found that buckyballs do exist in the two R Coronae Borealis stars in their sample that contain a fair amount of hydrogen. Studies published last year, including one by García-Hernández, showed that buckyballs were present in planetary nebulae rich in hydrogen. Together, these results tell us that fullerenes are much more abundant than previously believed, because they are formed in normal and common “hydrogen-rich” and not rare “hydrogen-poor” environments.
The current observations have changed our understanding of how buckyballs form. It suggests they are created when ultraviolet radiation strikes dust grains (specifically, “hydrogenated amorphous carbon grains”) or by collisions of gas. The dust grains are vaporized, producing an interesting chemistry where buckyballs and polycyclic aromatic hydrocarbons are formed. (The latter molecules of a variety of sizes are formed from carbon and hydrogen.) “In recent decades, a number of molecules and diverse dust features have been identified by astronomical observations in various environments. Most of the dust that determines the physical and chemical characteristics of the interstellar medium is formed in the outflows of asymptotic giant branch stars and is further processed when these objects become planetary nebulae.” says Jan Cami (et al). “We studied the environment of Tc 1, a peculiar planetary nebula whose infrared spectrum shows emission from cold and neutral C60 and C70. The two molecules amount to a few percent of the available cosmic carbon in this region. This finding indicates that if the conditions are right, fullerenes can and do form efficiently in space.”
Spiral galaxy NGC 247, shot with the Wide Field Imager at ESO’s La Silla Observatory in Chile. Credit: ESO
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One of our celestial neighbors, the spiral galaxy NGC 247, just moved about a million light-years closer.
Well, not really. But astronomers are retooling estimates of the distance to it, which was overestimated in the past partly because of the nearly edge-on tilt, shown above. The just-released image, from the Wide Field Imager on the MPG/ESO 2.2-metre telescope in Chile, shows large numbers of the galaxy’s component stars and glowing pink clouds of hydrogen, marking regions of active star formation, in the loose and ragged spiral arms. Numerous other galaxies can be seen in the distance.
Through a moderate-sized amateur telescope, the Cetus galaxy appears large but dim, and is seen best in a dark sky. Credit: ESO, IAU and Sky & Telescope
NGC 247 (RA 00h 47′ 14″ – 20deg 52′ 04″) is one of the closest spiral galaxies of the southern sky, now believed to lie about 11 million light-years away in the constellation Cetus (The Whale). It’s part of the Sculptor Group, a collection of galaxies associated with the Sculptor Galaxy (NGC 253, shown in previous releases here and here). This is the nearest group of galaxies to our Local Group, which includes the Milky Way.
To measure the distance from the Earth to a nearby galaxy, astronomers have to rely on a type of variable star called a Cepheid to act as a distance marker. Cepheids are very luminous stars, whose brightness varies at regular intervals. The time taken for the star to brighten and fade can be plugged into a simple mathematical relation that gives its intrinsic brightness. When compared with the measured brightness this gives the distance. However, this method isn’t foolproof, as astronomers think this period–luminosity relationship depends on the composition of the Cepheid.
Another problem arises from the fact that some of the light from a Cepheid may be absorbed by dust en route to Earth, making it appear fainter, and therefore further away than it really is. This is a particular problem for NGC 247 with its highly inclined orientation, as the line of sight to the Cepheids passes through the galaxy’s dusty disc.
However, a team of astronomers is currently looking into the factors that influence these celestial distance markers in a study called the Araucaria Project. The team has already reported that NGC 247 is more than a million light-years closer to the Milky Way than was previously thought, bringing its distance down to just over 11 million light-years.
More information about the lead image: It was created from a large number of monochrome exposures taken through blue, yellow/green and red filters taken over many years. In addition, exposures through a filter that isolates the glow from hydrogen gas have also been included and colored red. The total exposure time per filter was 20 hours, 19 hours, 25 minutes and 35 minutes, respectively.
Jane Houston Jones from JPL provides a video report on the happenings in space this month, and what you can see in the night sky in March: the MESSENGER spacecraft goes into orbit around Mercury on the 18th, and you can see the swift planet in the evening skies, too! Meanwhile, celebrate Sun-Earth day on the 19th, and view the sun through solar safe telescopes.
Earlier this year, I wrote an article about a Cepheid variable star named V19 in M31. This Cepheid was one that once pulsated strongly and was one of the variables Hubble first used to find the distance to the Andromeda galaxy. But today, V19 is a rare instance of a Cepheid that has seemingly, stopped pulsating. Another example of this phenomenon is that of Polaris, which has decreased in the amplitude of brightnesses by nearly an order of magnitude in the past century, although some reports indicate that it may be beginning to increase again. Meanwhile, a new paper is looking to add another star, HDE 344787, to this rare category and according to the paper, it may be “even more interesting than Polaris”.
The star in question, HDE 344787, is a F class supergiant. Although the variations in brightness have been difficult to observe, due to their small amplitude, astronomers have revealed two fundamental pulsation modes corresponding to 5.4 days and 3.8 days. But perhaps even more interesting, is that the 5.4 day period seems to be growing. Careful analysis of the data suggests that this period is growing by about 13 seconds per year. This finding is in strong agreement with what is predicted by models of stellar evolution for stars with metallicity similar to the sun passing through the instability strip for the first time.
HDE 344787 is similar in Polaris in that both stars share the same spectral type. However, the existence of two modes of pulsation is not seen in Polaris. The lengthening of the period of pulsation, however, is seen. For Polaris, its variation is growing by 4.5 seconds per year. Another similarity is that, like Polaris and V19, has been decreasing in the amplitudes of its brightness since at least 1890.
While the addition of this star to the collection of Cepheids that have decreased their amplitude, it does little to solve the mystery of why they might do so. Currently, both Polaris and HDE 344787 lie near the middle of the instability strip and, as such, are not simply evolving out of the region of instability. However, the confirmation of second pulsational mode may lend support to the notion that a change in one of these modes may serve to dampen the other, creating an effect known as the Blazhko Effect.
Ultimately, this star will require further observations to understand its nature better. Due the the faintness of this star (~10th magnitude) as well as the small change in brightness from the pulsations and the dense stellar field on which it lies, observations have been notoriously challenging.
It’s generally assumed that the Earth’s overall composition is similar to that of chondritic meteorites, the primitive, undifferentiated building blocks of the solar system. But a new study in Science Express led by Frederic Moynier, of the University of California at Davis, seems to suggest that Earth is a bit of an oddball.
Thin section of a chondritic meteorite. Credit: NASA
Moynier and his colleagues analyzed the isotope signature of chromium in a variety of meteorites, and found that it differed from chromium’s signature in the mantle.
“We show through high-precision measurements of Cr stable isotopes in a range of meteorites, which deviate by up to ~0.4‰ from the bulk silicate Earth, that Cr depletion resulted from its partitioning into Earth’s core with a preferential enrichment in light isotopes,” the authors write. “Ab-initio calculations suggest that the isotopic signature was established at mid-mantle magma ocean depth as Earth accreted planetary embryos and progressively became more oxidized.”
Chromium’s origins. New evidence suggests that, in the early solar nebula (A), chromium isotopes were divided into two components, one containing light isotopes, the other heavy isotopes. In the early Earth (B), these components formed a homogeneous mixture. During core partitioning (C), the core became enriched with lighter chromium isotopes, and the mantle with heavier isotopes. Courtesy of Science/AAAS
The results point to a process known as “core partitioning,” rather than an alternative process involving the volatilization of certain chromium isotopes so that they would have escaped from the Earth’s mantle. Core partitioning took place early on Earth at high temperatures, when the core separated from the silicate earth, leaving the core with a distinct composition that is enriched with lighter chromium isotopes, notes William McDonough, from the University of Maryland at College Park, in an accompanying Perspective piece.
McDonough writes that chromium, Earth’s 10th most abundant element, is named for the Greek word for color and “adds green to emeralds, red to rubies, brilliance to plated metals, and corrosion-proof quality to stainless steels.” It is distributed roughly equally throughout the planet.
He says the new result “adds another investigative tool for understanding and documenting past and present planetary processes. For the cosmochemistry and meteoritics communities, the findings further bolster the view that the solar nebula was a heterogeneous mixture of different components.”
Source: Science. The McDonough paper will be published online today by the journal Science, at the Science Express website.
Artist’s impression showing the disc around the young star T Chamaeleontis. The companion object in the foreground may be either a brown dwarf or a large planet. Credit: ESO/L. Calçada
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An international team of astronomers peering at a young star in the constellation Chamaeleon have detected a smaller companion — a dust-shrouded brown dwarf, or perhaps a planet — that appears to be carving out a large gap in the stellar disk. The discovery is a first: Although planets have been spotted before in more mature disks, this is the first detection of a planet-sized object in the disk around a young star.
Planets form from the disks of material around young stars, but the transition from dust disk to planetary system is rapid and few objects are caught during this phase. Astronomers are getting ever closer to glimpsing the births of planets, though — today’s announcement comes on the heels of a discovery last week using the Subaru Telescope in Hawaii, of a stellar disk around the star LkCa 15 similar in size to our own solar system, featuring rings and gaps possibly associated with the formation of giant planets.
T Chamaeleontis (RA 1h 04m 09.131s dec -76° 27′ 19.30″), T Cha for short, is a faint, young but sun-like star in the small southern constellation of Chamaeleon, about 350 light-years from Earth. T Cha is about seven million years old.
This chart shows the location of the young star T Cha within the constellation of Chamaeleon. The map shows most of the stars visible to the unaided eye under good conditions and the star itself is marked as a red circle. This star is too faint to see with the unaided eye, but is easily seen with a small telescope. Credit: ESO, IAU and Sky & Telescope
“Earlier studies had shown that T Cha was an excellent target for studying how planetary systems form,” said Johan Olofsson of the Max Planck Institute for Astronomy in Heidelberg, Germany, one of the lead authors of two related papers in the journal Astronomy & Astrophysics. “But this star is quite distant and the full power of the Very Large Telescope Interferometer was needed to resolve very fine details and see what is going on in the dust disk.”
The astronomers first observed T Cha using the AMBER instrument and the VLT Interferometer (VLTI). They found that some of the disk material formed a narrow dusty ring only about 20 million kilometers (12.4 million miles) from the star. Beyond this inner disk, they found a region devoid of dust with the outer part of the disk stretching out into regions beyond about 1.1 billion kilometers (683.5 million miles) from the star.
The ESO Very Large Telescope. Credit: ESO/G. Lombardi
“For us the gap in the dust disk around T Cha was a smoking gun,” said Nuria Huélamo, of the Centro de Astrobiología, ESAC in Spain, lead author of the second paper, “and we asked ourselves: could we be witnessing a companion digging a gap inside its protoplanetary disk?”
After further analysis, the team found the clear signature of an object located within the gap in the dust disk, about one billion kilometers, or 621 million miles, from the star — slightly further out than Jupiter is from our own sun.
The astronomers searched for the companion using NACO in two different spectral bands — at around 2.2 microns and 3.8 microns. The companion is only seen at the longer wavelength, which means that the object is either cool, like a planet, or a dust-shrouded brown dwarf.
Huélamo said he hopes future observations will reveal more about the companion and the disk, and explain what fuels the inner dusty disk.
Credit: X-ray: NASA/CXC/UNAM/Ioffe/D. Page, P. Shternin et al.; Optical: NASA/STScI; Illustration: NASA/CXC/M. Weiss
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NASA’s Chandra X-ray Observatory has discovered the first direct evidence for a superfluid, a bizarre, friction-free state of matter, at the core of a neutron star.
The image above, released today, shows X-rays from Chandra (red, green, and blue) and optical data from Hubble (gold) of Cassiopeia A, the remains of a massive star that exploded in a supernova. The evidence for superfluid has been found in the dense core of the star left behind, a so-called neutron star. The artist’s illustration in the inset shows a cut-out of the interior of the neutron star, where densities increase from the orange crust to the red core and finally to the inner red ball, the region where the superfluid exists.
Superfluids created in laboratories on Earth exhibit remarkable properties, such as the ability to climb upward and escape airtight containers. When they’re made of charged particles, superfluids are also superconductors, and they allow electric current to flow with no resistance. Such materials on Earth have widespread technological applications like producing the superconducting magnets used for magnetic resonance imaging [MRI].
Two independent research teams have used Chandra data to show that the interior of a neutron star contains superfluid and superconducting matter, a conclusion with important implications for understanding nuclear interactions in matter at the highest known densities. The teams publish their research separately in the journals Monthly Notices of the Royal Astronomical Society Letters and Physical Review Letters.
Cas A (RA 23h 23m 26.7s | Dec +58° 49′ 03.00) lies about 11,000 light-years away. Its star exploded about 330 years ago in Earth’s time-frame. A sequence of Chandra observations of the neutron star shows that the now compact object has cooled by about 4 percent over a ten-year period.
“This drop in temperature, although it sounds small, was really dramatic and surprising to see,” said Dany Page of the National Autonomous University in Mexico, leader of one of the two teams. “This means that something unusual is happening within this neutron star.”
Neutron stars contain the densest known matter that is directly observable; one teaspoon of neutron star material weighs six billion tons. The pressure in the star’s core is so high that most of the charged particles, electrons and protons, merge — resulting in a star composed mostly of neutrons.
The new results strongly suggest that the remaining protons in the star’s core are in a superfluid state and, because they carry a charge, also form a superconductor.
Both teams show that the rapid cooling in Cas A is explained by the formation of a neutron superfluid in the core of the neutron star within about the last 100 years as seen from Earth. The rapid cooling is expected to continue for a few decades, and then it should slow down.
“It turns out that Cas A may be a gift from the Universe because we would have to catch a very young neutron star at just the right point in time,” said Page’s co-author Madappa Prakash, from Ohio University. “Sometimes a little good fortune can go a long way in science.”
The onset of superfluidity in materials on Earth occurs at extremely low temperatures near absolute zero, but in neutron stars, it can occur at temperatures near a billion degrees Celsius. Until now there was a very large uncertainty in estimates of this critical temperature. This new research constrains the critical temperature to between one half a billion to just under a billion degrees.
Cas A will allow researchers to test models of how the strong nuclear force, which binds subatomic particles, behaves in ultradense matter. These results are also important for understanding a range of behavior in neutron stars, including “glitches,” neutron star precession and pulsation, magnetar outbursts and the evolution of neutron star magnetic fields.
Betelgeuse is a red super-giant, meaning it has enough mass that it will end as a supernova, rather than as a white dwarf with a planetary nebula. New research suggests that the star could've consumed a smaller companion star. Image credit: Hubble Space Telescope
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While planets orbiting twin stars are a staple of science fiction, another is having humans live on planets orbiting red giant stars. The majority of the story of Planet of the Apes takes place on a planet around Betelgeuse. Planets around Arcturus in Isaac Asimov’s Foundation series make up the capital of his Sirius Sector. Superman’s home planet was said to orbit a the fictional red giant, Rao. Races on these planets are often depicted as being old and wise since their stars are aged, and nearing the end of their lives. But is it really plausible to have such planets?
Stars don’t last forever. Our own Sun has an expiration date in about 5 billion years. At that time, the amount of hydrogen fuel in the core of the Sun will have run out. Currently, the fusion of that hydrogen into helium is giving rise to a pressure which keeps the star from collapsing in on itself due to gravity. But, when it runs out, that support mechanism will be gone and the Sun will start to shrink. This shrinking causes the star to heat up again, increasing the temperature until a shell of hydrogen around the now exhausted core becomes hot enough to take up the job of the core and begins fusing hydrogen to helium. This new energy source pushes the outer layers of the star back out causing it to swell to thousands of times its previous size. Meanwhile, the hotter temperature to ignite this form of fusion will mean that the star will give off 1,000 to 10,000 times as much light overall, but since this energy is spread out over such a large surface area, the star will appear red, hence the name.
So this is a red giant: A dying star that is swollen up and very bright.
Now to take a look at the other half of the equation, namely, what determines the habitability of a planet? Since these sci-fi stories inevitably have humans walking around on the surface, there’s some pretty strict criteria this will have to follow.
First off, the temperature must be not to hot and not to cold. In other words, the planet must be in the Habitable zone also known as the “Goldilocks zone”. This is generally a pretty good sized swath of celestial real estate. In our own solar system, it extends from roughly the orbit of Venus to the orbit of Mars. But what makes Mars and Venus inhospitable and Earth relatively cozy is our atmosphere. Unlike Mars, it’s thick enough to keep much of the heat we receive from the sun, but not too much of it like Venus.
This diagram shows the distances of the planets in the Solar System (upper row) and in the Gliese 581 system (lower row), from their respective stars (left). The habitable zone is indicated as the blue area, showing that Gliese 581 d is located inside the habitable zone around its low-mass red star. Based on a diagram by Franck Selsis, Univ. of Bordeaux. Credit: ESO
The atmosphere is crucial in other ways too. Obviously it’s what the intrepid explorers are going to be breathing. If there’s too much CO2, it’s not only going to trap too much heat, but make it hard to breathe. Also, CO2 doesn’t block UV light from the Sun and cancer rates would go up. So we need an oxygen rich atmosphere, but not too oxygen rich or there won’t be enough greenhouse gasses to keep the planet warm.
The problem here is that oxygen rich atmospheres just don’t exist without some assistance. Oxygen is actually very reactive. It likes to form bonds, making it unavailable to be free in the atmosphere like we want. It forms things like H2O, CO2, oxides, etc… This is why Mars and Venus have virtually no free oxygen in their atmospheres. What little they do comes from UV light striking the atmosphere and causing the bonded forms to disassociate, temporarily freeing the oxygen.
Earth only has as much free oxygen as it does because of photosynthesis. This gives us another criteria that we’ll need to determine habitability: the ability to produce photosynthesis.
So let’s start putting this all together.
Firstly, the evolution of the star as it leaves the main sequence, swelling up as it becomes a red giant and getting brighter and hotter will mean that the “Goldilocks zone” will be sweeping outwards. Planets that were formerly habitable like the Earth will be roasted if they aren’t entirely swallowed by the Sun as it grows. Instead, the habitable zone will be further out, more where Jupiter is now.
However, even if a planet were in this new habitable zone, this doesn’t mean its habitable under the condition that it also have an oxygen rich atmosphere. For that, we need to convert the atmosphere from an oxygen starved one, to an oxygen rich one via photosynthesis.
So the question is how quickly can this occur? Too slow and the habitable zone may have already swept by or the star may have run out of hydrogen in the shell and started contracting again only to ignite helium fusion in the core, once again freezing the planet.
The only example we have so far is on our own planet. For the first three billion years of life, there was little free oxygen until photosynthetic organisms arose and started converting it to levels near that of today. However, this process took several hundred million years. While this could probably be increased by an order of magnitude to tens of millions of years with genetically engineered bacteria seeded on the planet, we still need to make sure the timescales will work out.
It turns out the timescales will be different for different masses of stars. More massive stars burn through their fuel faster and will thus be shorter. For stars like the Sun, the red giant phase can last about 1.5 billion years, so ~100x longer than is necessary to develop an oxygen rich atmosphere. For stars twice as massive as the Sun, that timescale drops to a mere 40 million years, approaching the lower limit of what we’ll need. More massive stars will evolve even more quickly. So for this to be plausible, we’ll need lower mass stars that evolve slower. A rough upper limit here would be a two solar mass star.
However, there’s one more effect we need to worry about: Can we have enough CO2 in the atmosphere to even have photosynthesis? While not nearly as reactive as oxygen, carbon dioxide is also subject to being removed from the atmosphere. This is due to effects like silicate weathering such as CO2 + CaSiO3 –> CaCO3 + SiO2. While these effects are slow they build up with geological timescales. This means we can’t have old planets since they would have had all their free CO2 locked away into the surface. This balance was explored in a paper published in 2009 and determined that, for an Earth mass planet, the free CO2 would be exhausted long before the parent star even reached the red giant phase!
So we’re required to have low mass stars that evolve slowly to have enough time to develop the right atmosphere, but if they evolve that slowly, then there’s not enough CO2 left to get the atmosphere anyway! We’re stuck with a real Catch 22. The only way to make this feasible again is to find a way to introduce sufficient amounts of new CO2 into the atmosphere just as the habitable zone starts sweeping by.
Fortunately, there are some pretty large repositories of CO2 just flying around! Comets are composed mostly of frozen carbon monoxide and carbon dioxide. Crashing a few of them into a planet would introduce sufficient CO2 to potentially get photosynthesis started (once the dust settled down). Do that a few hundred thousand years before the planet would enter the habitable zone, wait ten million years, and then the planet could potentially be habitable for as much as an additional billion years more.
Ultimately this scenario would be plausible, but not exactly a good personal investment since you’d be dead long before you’d be able to reap the benefits. A long term strategy for the survival of a space faring species perhaps, but not a quick fix to toss down colonies and outposts.
Artist’s rendering of the environment around the supermassive black hole at the center of Mrk 231. The broad outflow seen in the Gemini data is shown as the fan-shaped wedge at the top of the accretion disk around the black hole, in side view. A similar outflow is probably present under the disk as well. The total amount of material entrained in the broad flow is at least 400 times the mass of the sun per year. Credit: Gemini Observatory/AURA, artwork by Lynette Cook
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Astronomers have long suspected that something must stymie actively growing black holes, because most galaxies in the local universe don’t have them. Now, the Gemini Observatory has captured a galactic check-and-balance — a large-scale quasar outflow in the galaxy Markarian 231 that appears to be depriving a supermassive black hole its diet of gas and dust.
The work is a collaboration between David Rupke of Rhodes College in Tennessee and the University of Maryland’s Sylvain Veilleux. The results are to be published in the March 10 issue of The Astrophysical Journal Letters.
Markarian 231 (12h56’14.23″ +56d52’25.24″) is located about 600 million light-years away in the direction of the constellation of Ursa Major. Although its mass is uncertain, some estimates indicate that Mrk 231 has a mass in stars about three times that of the Milky Way, and its central black hole is estimated to have a mass of at least 10 million solar masses or also about three times that of the supermassive black hole in the Milky Way.
Theoretical modeling specifically points to quasar outflows as the counterbalance to black hole growth. In this negative feedback loop, while the black hole is actively acquiring mass as a quasar, the outflows carry away energy and material, suppressing further growth. Small-scale outflows had been observed before, but none sufficiently powerful to account for this predicted and fundamental aspect of galaxy evolution. The Gemini observations provide the first clear evidence for outflows powerful enough to support the process necessary to starve the galactic black hole and quench star formation by limiting the availability of new material.
This extraction from the data cube shows the large-scale, fast outflow of neutral sodium at the center of the quasar Markarian 231. We are looking down onto the material that moves toward us relative to the galaxy, so the measured velocities are negative. The large black circle marks the location of the black hole, and red lines show the location of a radio jet. In addition to the quasar outflow, the jet pushes the material at the top right, resulting in even greater speeds. Part of the starburst is located at the position of the box at the lower left, and it is likely responsible for the gas motion in this region.
Study author Veilleux says Mrk 231 is an ideal laboratory for studying outflows caused by feedback from supermassive black holes: “This object is arguably the closest and best example that we know of a big galaxy in the final stages of a violent merger and in the process of shedding its cocoon and revealing a very energetic central quasar. This is really a last gasp of this galaxy; the black hole is belching its next meals into oblivion!” As extreme as Mrk 231’s eating habits appear, Veilleux adds that they are probably not unique: “When we look deep into space and back in time, quasars like this one are seen in large numbers, and all of them may have gone through shedding events like the one we are witnessing in Mrk 231.”
Although Mrk 231 is extremely well studied, and known for its collimated jets, the Gemini observations exposed a broad outflow extending in all directions for at least 8,000 light-years around the galaxy’s core. The resulting data reveal gas (characterized by sodium, which absorbs yellow light) streaming away from the galaxy center at speeds of over 1,000 kilometers per second. At this speed, the gas could go from New York to Los Angeles in about 4 seconds. This outflow is removing gas from the nucleus at a prodigious rate — more than 2.5 times the star formation rate. The speeds observed eliminate stars as the possible “engine” fueling the outflow. This leaves the black hole itself as the most likely culprit, and it can easily account for the tremendous energy required.
The energy involved is sufficient to sweep away matter from the galaxy. However, “when we say the galaxy is being blown apart, we are only referring to the gas and dust in the galaxy,” notes Rupke. “The galaxy is mostly stars at this stage in its life, and the outflow has no effect on them. The crucial thing is that the fireworks of new star formation and black hole feeding are coming to an end, most likely as a result of this outflow.”
Source: Gemini press release. The paper appears here. See also some galactic merger animations, courtesy of the Harvard-Smithsonian Center for Astrophysics.
