Astronomy Archives

January 28, 2015December 23, 2015 by Vanessa Janek

Astronomers See a Massive Black Hole Tear a Star Apart

When a star encounters a black hole, tidal forces stretch the star into an elongated blob before tearing it apart, as seen in these images from a computer simulation by James Guillochon of Harvard University.

A telescope peers into the blackness of deep space. Suddenly – a brilliant flash of light appears that wasn’t there before. What could it be? A supernova? Two massively dense stars fusing together? Perhaps a gamma ray burst?

Five years ago, researchers using the ROTSE IIIb telescope at McDonald Observatory noticed just such an event. But far from being your run-of-the-mill stellar explosion or neutron star merger, the astronomers believe that this tiny flare was, in fact, evidence of a supermassive black hole at the center of a distant galaxy, tearing a star to shreds.

Astronomers at McDonald had been using the telescope to scan the skies for such nascent flashes for years, as part of the ROTSE Supernova Verification Project (SNVP). And at first blush, the event seen in early 2009, which the researches nicknamed “Dougie,” looked just like many of the other supernovae they had discovered over the course of the project. With a blazing – 22.5-magnitude absolute brightness, the event fit squarely within the class of superluminous supernovae that the researchers were already familiar with.

But as time went on and more data on Dougie rolled in, the astronomers began to change their minds. X-ray observations made by the orbiting Swift satellite and optical spectra taken by McDonald’s Hobby-Eberly Telescope revealed an evolving light curve and chemical makeup that didn’t fit with computer simulations of superluminous supernovae. Likewise, Dougie didn’t appear to be a neutron star merger, which would have reached peak luminosity far more quickly than was observed, or a gamma ray burst, which, even at an angle, would have appeared far brighter in x-ray light.

That left only one option: a so-called “tidal disruption event,” or the carnage and spaghettification that occurs when a star wanders too close to a black hole’s horizon. J. Craig Wheeler, head of the supernova group at The University of Texas at Austin and a member of the team that discovered Dougie, explained that at short distances, a black hole’s gravity exerts a much stronger pull on the side of the star nearest to it than it does on the star’s opposite side. He explained, “These especially large tides can be strong enough that you pull the star out into a noodle.”

The team refined their models of the event and came to a surprising conclusion: having drawn in Dougie’s stellar material a bit faster than it could handle, the black hole was now “choking” on its latest meal. This is due to an astrophysical principle called the Eddington Limit, which states that a black hole of a given size can only handle so much infalling material. After this limit has been reached, any additional intake of matter exerts more outward pressure than the black hole’s gravity can compensate for. This pressure increase has a kind of rebound effect, throwing off material from the black hole’s accretion disk along with heat and light. Such a burst of energy accounts for at least part of Dougie’s brightness, but also indicates that the original dying star – a star not unlike our own Sun – wasn’t going down without a fight.

Combining these observations with the mathematics of the Eddington Limit, the researchers estimated the black hole’s size to be about 1 million solar masses – a rather small black hole, at the center of a rather small galaxy, three billion light years away. Discoveries like these not only allow astronomers to better understand the physics of black holes, but also properties of their often unassuming home galaxies. After all, mused Wheeler, “Who knew this little guy had a black hole?”

To get a simulated glimpse of Dougie for yourself, check out the amazing animation below, courtesy of team member James Guillochon:

The research is published in this month’s issue of The Astrophysical Journal. A pre-print of the paper is available here.

January 27, 2015December 23, 2015 by David Dickinson

Luna vs. the Hyades! The 1st of 13 Occultations of Aldebaran Set For January 29th

The cosmos is continually in motion.

Be it atoms, stars or snowflakes from the latest nor’easter pounding the New England seaboard, anything worth studying involves movement. And as skies and snowbound roads clear, this Wednesday and Thursday evening will give us a reason to brave the January cold, as the waxing gibbous Moon pierces the Hyades star cluster to graze past the bright star Aldebaran.

During Thursday night’s passage, the Moon will be 78% illuminated. In a sort ‘cosmos mimics controversy’ irony, the gibbous Moon is doing its best to mimic a sky bound ‘deflategate’ football just in time for Superbowl XLIX this weekend.

The motion of the Moon this week across the Hyades. Credit: Stellarium.

But the January 29^th event also marks the first occultation of Aldebaran for 2015.

Fun fact: At magnitude +0.8, Aldebaran is the only star brighter than +1^st magnitude north of the celestial equator that the Moon can currently occult. Regulus, the runner up, shines at magnitude +1.4. Two other second magnitude stars — Antares and Spica — lie along the Moon’s path on occasion, and up until the 2^nd century BC, it was possible for the Moon to occult Pollux in the constellation Gemini as well.

There are 13 occultations of Aldebaran in 2015, and the Moon occults the star 49 times overall until the last event in the current cycle on September 3^rd, 2018. Aldebaran is also occulted by the Moon more often in the current 2010-2020 decade than any other bright star. You can even spy Aldebaran near the daytime Moon with binoculars, as we did back in 1996 from North Pole, Alaska.

Maps for the 13 occultations of Aldebaran by the Moon in 2015, click to enlarge. solid lines denote regions were the occultation occurs under dark skies. Credit: Occult 4.0.

Of course, the January 29^th event is an occultation only for the high Arctic, with only a scattering of villages and distant early warning stations along the northern Nunavut coast welcoming the sequence of 2015 occultations of the bright star.

The rest of us will see a close photogenic pass, as the Moon makes an end run through the Hyades star cluster every 27.3 day sidereal lunar month in 2015. The Moon will thus occult several members of the Hyades on each pass. Our best bet for North America is the occultation of Aldebaran on November 26^th, though the Moon will be just 13 hours past Full.

68 Tauri. Credit: Occult 4.0 — The occultation of 68 Tauri (a member of the Hyades) for January 29th. Credit: Occult 4.0.

Why doesn’t the path of the Moon just stay put with respect to the sky? Because the orbit of our Moon is fixed at an inclination of 5.1 degrees not with respect to our equator, but to the plane of the ecliptic. This means that the Moon’s orbit is in motion as well, and can wander anywhere from declination 28.6 degrees north to south as it cycles from a shallow to steep path every 18.6 years. We’re actually in a shallow year in 2015 (known as a minor lunar standstill) after which the apparent path of the Moon through the sky begins to widen again until April 2025.

An occultation is celestial motion that you can see in real time as a star or planet is photobomb’d by the onrushing Moon like a January snowplow… but those background stars are in motion as well.

The Hyades themselves — along with our own solar system — are moving around the galactic center. The nearest open cluster to us at 153 light years distant, the Hyades provided a unique object of study for 19^th century astronomers. Astronomer Lewis Boss of the Dudley observatory spent several decades studying the proper motion — the apparent motion that a star seems to be moving across the sky from our solar system-bound perspective, measured in arc seconds — of the Hyades, and found the entire group was converging on a point in the constellation Orion near 6 hours 7’ right ascension and +7 degrees declination.

The imaginary convergent point of the Hyades in the night sky. Credit: Starry Night Education software.

Of course, this motion is relative and demonstrates a changing perspective, as the Hyades recedes from our solar system like a defensive line rushing to sack a quarterback.

OK, enough with the sports similes. The Hyades are so close that the actual Hyades Stream — often referred to as the Hyades Moving Group — is actually strewn across the constellations Orion, Taurus and Aries and more.

Some stars, such as 20 Arietis in the adjacent constellation Aries and Iota Horologii in the southern hemisphere may actually members as well. There’s always a bit of ongoing controversy when it comes to actual moving group membership, which is usually pegged by determining proper motion, coupled with the age and metallicity of prospective stars. Growing up in the Milky Way galaxy, our Sun was once a member of some unnamed ancient open cluster that has since long dispersed, like the Hyades are in the process of doing now.

The asterism of the Hyades and the ‘eye of the Bull.’ Photo by author.

The Hyades contains hundreds of stars and ironically, Aldebaran is not a member of the cluster, but is merely 65 light years away from us in the foreground. The V-shaped asterism of the Hyades gives the Head of Taurus the Bull its distinctive shape. The Hyades are named after the rain nymph daughters of Atlas from Greek mythology, whose half daughters the Pleiades also adorn the nearby sky.

And as an added bonus, don’t miss comet C/2014 Q2 Lovejoy crossing the constellation Triangulum, also nearby. Q2 Lovejoy reaches perihelion this week on January 30th, and although it’s completing with the evening Moon, it’s still holding out at a respectable magnitude +4.5.

All reasons to get out these chilly January evenings and ponder a hurried universe continually in motion, both fast and slow.

-Check out Q2 Lovejoy on January 30th courtesy of the Virtual Telescope project.

January 26, 2015December 23, 2015 by Morgan Rehnberg

Are Asteroids the Future of Planetary Science?

The asteroid Vesta as seen by the Dawn spacecraft. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA

I don’t think I ever learned one of those little rhymes – My Very Educated Mother Just Served Us Nine Pizzas – to memorize the order of the planets, but if I had, it would’ve painted for me a minimalist picture of the solar system. (Side question: what is my Very Educated Mother serving now that we only have Dwarf Pizzas?) After all, much of the most exciting work in planetary science today happens not at the planets, but around them.

Ask an astronomer where in the solar system she’d like to visit next and you’re just as likely to hear Europa, Enceladus, Titan, or Triton as you are Venus, Mars, or Neptune. Our solar system hosts eight planets but nearly 200 known moons. And moons, it turns out, are just the start. We’ve detected more than a million asteroids; surely that’s just a fraction of what’s lurking beyond our limits of observation. Let’s not even think about the billions, perhaps even trillions, of Kuiper belt and Oort cloud objects – we could be here all day! So, while the planets may dominate the solar system gravitationally, they are pitiful numerically.

If there is one thing that the study of exoplanets has taught us in the last twenty years, it’s that the Universe thrives on chance. Given enough planets (and there appear to be gazillions out there!), practically anything can happen. Want a planet with a double sunset? We’ve got that, but perhaps you’d prefer one with three! How about a planet whose temperature is nearly half that of the surface of the Sun? No problem there. I can even offer you a planet ten times more massive than Jupiter, but nearly 20 times closer to its star than Mercury (probably not the best place for your first off-world vacation home…). The point is, with only a few thousand planets discovered, what we’ve seen already is astonishing. Imagine what those million asteroids could be hiding.

In fact, asteroids might be the next great frontier in planetary science. Let’s find out why.

An artist's impression of the rings around Chariklo. Credit: ESO/L. Calçada/M. Kornmesser/Nick Risinger (skysurvey.org) — An artist’s impression of the rings around Chariklo. Credit:
ESO/L. Calçada/M. Kornmesser/Nick Risinger (skysurvey.org)

Suppose I ask you to think about the planet Saturn. What’s the first thing that jumps to mind? Probably its rings. And, if you were paying attention around the time you learned one of those nifty rhymes, you might recall that Jupiter, Uranus, and Neptune also have rings. But, did you know that at least one asteroid is also home to a ring system? Called Chariklo, it’s the largest known of a family of asteroids trapped between the orbits of the outer planets. Early last year, astronomers reported the detection of a ring system about this 250-kilometer sized object. I say a ring system because there appear to be at least two distinct rings encircling Chariklo. Discovering this new system is more than just an additional data point. Perhaps the paramount question facing the field of planetary rings today is how they formed and how long they can last; the existence of rings around a tiny asteroid tells a very different story than that implied by the giant planets.

Of course, rings haven’t been the biggest planetary science story of the last decade (much to my chagrin as a rings researcher!). That honor might instead lie with geysers. The 2005 discovery of an enormous water plume emanating from the surface of Saturn’s moon Enceladus changed the way we looked at the icy moons of the solar system. Eight years later, astronomers using Hubble claimed to have found a similar phenomenon at Jupiter’s moon Europa (now they’re not so sure). But geysers, too, might not be the sole province of planetary moons. Just last year, researchers with the Herschel Space Telescope found the first evidence for water vapor emanating from the surface of the enormous asteroid Ceres! There’s more good news: unlike Europa, with its off-in-the-future mission, the Dawn spacecraft is on its way to Ceres right now. It will arrive in just under two months and provide a close-up look at the second confirmed off-world geyser.

Speaking of moons, it probably won’t surprise you to learn that asteroids have those, too! In fact, the number of asteroids with known satellites is far too long to enumerate here. But, they are not merely numerous; the variety of asteroid moons seems to be nearly as large as the variety of asteroids themselves. Like with the planets, many asteroids dwarf their moons. Others, though, are more like binary systems in which both bodies are approximately the same size. And, although we generally know little about their shape, the variety in this realm also appears tremendous.

An artist's conception of how an unmanned spacecraft might redirect an asteroid into lunar orbit. Credit: NASA — An artist’s conception of how an unmanned spacecraft might redirect an asteroid into lunar orbit. Credit: NASA

Ultimately, though, it’s not their number or their variety that might make asteroids the future of planetary science; the laws of physics are on their side. It’s no accident that NASA intends to send astronauts to land on an asteroid long before they attempt to touch down on Mars. Neither is it a coincidence that at least three missions (Hayabusa, Hayabusa 2, and OSIRIS-REx) will have returned, or at least attempted to, samples from an asteroid to the Earth before NASA’s ambitious plan to do the same at Mars. The gravitational tug on the surface of the Red Planet is more than thirteen times more powerful than that of even the largest asteroid.

We’re seeing this accessibility in action already. Hayabusa returned a sample of asteroid Itokawa back in 2010 and its successor is already on its way. And, remember Dawn on its way to Ceres? It turns out that wasn’t its first stop. Before setting out for the solar system’s largest asteroid, the mission spent fourteen months in orbit about the asteroid Vesta. When it arrives at Ceres in March, Dawn will become the first spacecraft in history to orbit two extraterrestrial bodies.

Dawn is, I think, a signal of things to come. Asteroids, in general, and the main asteroid belt, in particular, offer the tantalizing opportunity to visit a variety of different worlds in one fell swoop. These are places that are closer to us, easier to approach, and just as scientifically interesting as the classical celestial worlds. Does this mean that the world’s science agencies will or even should abandon the study of the planets? Of course not. No asteroid looks like the cloud tops of Jupiter or the methane lakes of Titan or the intense heat of Venus. I’m not at all trying to limit the worlds which we visit. Quite the opposite, in fact: we’ve suddenly found a million new places to go!

January 26, 2015December 23, 2015 by Vanessa Janek

Astronomers Catch A Quasar Shutting Off

This artist's rending shows "before" and "after" images of a changing look quasar. Credit: Yale University.

Last week, astronomers at Yale University reported seeing something unusual: a seemingly stedfast beacon from the far reaches of the Universe went quiet. This relic light source, a quasar located in the region of our sky known as the celestial equator, unexpectedly became 6-7 times dimmer over the first decade of the 21st century. Thanks to this dramatic change in luminosity, astronomers now have an unprecedented opportunity to study both the life cycle of quasars and the galaxies that they once called home.

A quasar arises from a distant (and therefore, very old) galaxy that once contained a central, rotating supermassive black hole – what astronomers call an active galactic nucleus. This spinning beast ravenously swallowed up large amounts of ambient gas and dust, kicking up surrounding material and sending it streaming out of the galaxy at blistering speeds. Quasars shine because these ancient jets achieved tremendous energies, thereby giving rise to a torrent of light so powerful that astronomers are still able to detect it here on Earth, billions of years later.

In their hey-day, some active galactic nuclei were also energetic enough to excite electrons farther away from the central black hole. But even in the very early Universe, electrons couldn’t withstand that kind of excitement forever; the laws of physics don’t allow it. Eventually, each electron would drop back down to its rest state, releasing a photon of corresponding energy. This cycle of excitation happened over and over and over again, in regular and predictable patterns. Modern astronomers can visualize those transitions – and the energies that caused them – by examining a quasar’s optical spectrum for characteristic emission lines at certain wavelengths.

An example of an atomic spectrum, showing emission lines at particular wavelengths. — A simple example of an atomic spectrum, showing emission lines at particular wavelengths. Broad humps correspond to brighter emission lines, while lines that arise from narrow, lower-intensity emissions appear dimmer. Credit: NASA

Not all quasars are created equal, however. While the spectra of some quasars reveal many bright, broad emission lines at different energies, other quasars’ spectra consist of only the dim, narrow variety. Until now, some astronomers thought that these variations in emission lines among quasars were simply due to differences in their orientation as seen from Earth; that is, the more face-on a quasar was relative to us, the broader the emission lines astronomers would be able to see.

But all of that has now been thrown into question, thanks to our friend J015957.64+003310.5, the quasar revealed by the team of astronomers at Yale. Indeed, it is now plausible that a quasar’s pattern of emission lines simply changes over its lifetime. After gathering ten years of spectral observations from the quasar, the researchers observed its original change in brightness in 2010. In July 2014, they confirmed that it was still just as dim, disproving hypotheses that suggested the effect was simply due to intervening gas or dust. “We’ve looked at hundreds of thousands of quasars at this point, and now we’ve found one that has switched off,” explained C. Megan Urry, the study’s co-author.

How would that happen, you ask? After observing the comparable dearth of broad emission lines in its spectrum, Urry and her colleagues believe that long ago, the black hole at the heart of the quasar simply went on a diet. After all, an active galactic nucleus that consumed less material would generate less energy, giving rise to fainter particle jets and fewer excited atoms. “The power source just went dim,” said Stephanie LaMassa, the study’s principal investigator.

LaMassa continued, “Because the life cycle of a quasar is one of the big unknowns, catching one as it changes, within a human lifetime, is amazing.” And since the life cycle of quasars is dependent on the life cycle of supermassive black holes, this discovery may help astronomers to explain how those that lie at the center of most galaxies evolve over time – including Sagittarius A*, the supermassive black hole at the center of our own Milky Way.

“Even though astronomers have been studying quasars for more than 50 years, it’s exciting that someone like me, who has studied black holes for almost a decade, can find something completely new,” added LaMassa.

The team’s research will be published in an upcoming issue of The Astrophysical Journal. A pre-print of the paper is available here.

January 26, 2015December 23, 2015 by Elizabeth Howell

What Are The Benefits Of Space Exploration?

Eugene Cernan on the lunar surface, December 13, 1972. Credit: NASA.

Why explore space? It’s an expensive arena to play in, between the fuel costs and the technological challenge of operating in a hostile environment. For humans, a small mistake can quickly become fatal — something that we have seen several times in space history. And for NASA’s budget, there are projects that come in late and over budget, drawing the ire of Congress and the public.

These are some of the drawbacks. But for the rest of this article, we will focus on some of the benefits of going where few humans have gone before.

Spinoffs

Perhaps the most direct benefit comes from technologies used on Earth that were first pioneered in space exploration. This is something that all agencies talk about, but we’ll focus on the NASA Spinoff program as an example. (NASA will be used as the prime example for most of this article, but many of these cited benefits are also quoted by other space agencies.)

The program arose from NASA’s desire to showcase spinoffs at congressional budget hearings, according to its website. This began with a “Technology Utilization Program Report” in 1973, which began as a black-and-white circular and progressed to color in 1976 following public interest. Since that year, NASA has published more than 1,800 reports on spinoffs.

The agency has several goals in doing this. “Dispelling the myth of wasted taxpayer dollars” is one NASA cites, along with encouraging the public to follow space exploration and showing how American ingenuity can work in space.

There are many commercialized advances the program says it contributed to, including “memory foam” (first used for airline crash protection), magnetic resonance imaging and smoke detection. In many cases, NASA did not invent the technology itself, but just pushed it along, the agency says.

An MRI image of the lower back. Credit: NASA

But as counterpoint to NASA’s arguments, some critics argue the technology would have been developed anyway without space exploration, or that the money spent on exploration itself does not justify the spinoff.

Job creation

Another popularly cited benefit of space exploration is “job creation”, or the fact that a space agency and its network of contractors, universities and other entities help people stay employed. From time to time, NASA puts out figures concerning how many associated jobs a particular project generates, or the economic impact.

Here’s an example: in 2012, NASA administrator Charles Bolden published a blog post about the Curiosity Mars rover landing, which was picked up by the White House website. “It’s also important to remember that the $2.5 billion investment made in this project was not spent on Mars, but right here on Earth, supporting more than 7,000 jobs in at least 31 states,” he wrote.

Hazcam fisheye camera image shows Curiosity drilling into “Windjana” rock target on April 29, 2014 (Sol 615). Flattened and colorized image shows Mount Remarkable butte backdrop. Credit: NASA/JPL/Marco Di Lorenzo/Ken Kremer - kenkremer.com — Hazcam fisheye camera image shows Curiosity drilling into “Windjana” rock target on April 29, 2014 (Sol 615). Flattened and colorized image shows Mount Remarkable butte backdrop. Credit: NASA/JPL/Marco Di Lorenzo/Ken Kremer – kenkremer.com

But the benefit can cut in a negative way, too. NASA’s budget is allocated by Congress, which means that the amount of money it has available for employment fluctuates. There are also some programs that are highly dependent on grants, which can make stable jobs challenging in those fields. Finally, as the priorities of Congress/NASA change, jobs can evaporate with it. One example was the space shuttle’s retirement, which prompted a job loss so massive that NASA had a “transition strategy” for its employees and contractors.

It’s also unclear what constitutes a “job” under NASA parlance. Some universities have researchers working on multiple projects — NASA-related or not. Employment can also be full-time, part-time or occasional. So while “job creation” is cited as a benefit, more details about those jobs are needed to make an informed decision about how much good it does.

Education

Teaching has a high priority for NASA, so much so that it has flown astronaut educators in space. (The first one, Christa McAuliffe, died aboard the space shuttle Challenger during launch in 1986. Her backup, Barbara Morgan, was selected as an educator/mission specialist in 1998 and flew aboard STS-118 in 2007.) And to this day, astronauts regularly do in-flight conferences with students from space, ostensibly to inspire them to pursue careers in the field.

Christa McAuliffe and Barbara Morgan practice teaching from space. Credit: "The Lost Lessons" — Christa McAuliffe and Barbara Morgan practice teaching from space. Credit: “The Lost Lessons”

NASA’s education office has three goals: making the workforce stronger, encouraging students to pursue STEM careers (science, technology, engineering and mathematics), and “engaging Americans in NASA’s mission.” Other space agencies also have education components to assist with requirements in their own countries. It’s also fair to say the public affairs office for NASA and other agencies play roles in education, although they also talk about topics such as missions in progress.

But it’s hard to figure out how well the education efforts translate into inspiring students, according to a National Research Council report on NASA’s primary and secondary education program in 2008. Among other criticisms, the program was cited as unstable (as it needs to change with political priorities) and there was little “rigorous evaluation” of its effectiveness. But NASA’s emphasis on science and discovery was also praised.

Anecdotally, however, many astronauts and people within NASA have spoken about being inspired by watching missions such as Apollo take place. And the same is true of people who are peripherally involved in the field, too. (A personal example: this author first became interested in space in the mid-1990s through the movie Apollo 13, which led to her watching the space shuttle program more closely.)

New Rosetta mission findings do not exclude comets as a source of water in and on the Earth's crust but does indicate comets were a minor contribution. A four-image mosaic comprises images taken by Rosetta’s navigation camera on 7 December from a distance of 19.7 km from the centre of Comet 67P/Churyumov-Gerasimenko. (Credit: ESA/Rosetta/Navcam Imager) — New Rosetta mission findings do not exclude comets as a source of water in and on the Earth’s crust but does indicate comets were a minor contribution. A four-image mosaic comprises images taken by Rosetta’s navigation camera on 7 December from a distance of 19.7 km from the centre of Comet 67P/Churyumov-Gerasimenko. (Credit: ESA/Rosetta/Navcam Imager)

Intangible benefits

Added to this host of business-like benefits, of course, are the intangibles. What sort of value can you place on better understanding the universe? Think of finding methane on Mars, or discovering an exoplanet, or constructing the International Space Station to do long-term exploration studies. Each has a cost associated with it, but with each also comes a smidgeon of knowledge we can add to the encyclopedia of the human race.

Space can also inspire art, which is something seen heavily in 2014 following the arrival of the European Space Agency Rosetta mission at Comet 67P/Churyumov–Gerasimenko. It inspired songs, short videos and many other works of art. NASA’s missions, particularly those early space explorers of the 1950s and 1960s, inspired creations from people as famous as Norman Rockwell.

There also are benefits that maybe we cannot anticipate ahead of time. The Search for Extraterrestrial Intelligence (SETI) is a network that advocates looking for life around the universe, likely because communicating with beings outside of Earth could bring us some benefit. And perhaps there is another space-related discovery just around the corner that will change our lives drastically.

For more information, here is a Universe Today article about how we really watched television from the moon. We also collected some spin-offs from the Hubble Space Telescope. You can also listen to Astronomy Cast. Episode 144 Space Elevators.

January 24, 2015December 23, 2015 by Bob King

Latest Research Reveals a Bizarre and Vibrant Rosetta’s Comet

Dust-covered, boulder-strewn landscape on the smaller of the two lobes of Comet 67P/Churyumov-Gerasimenko taken from a distance of 5 miles (8 km). Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

We’ve subsisted for months on morsels of information coming from ESA’s mission to Comet 67P/Churyumov-Gerasimenko. Now, a series of scientific papers in journal Science offers a much more complete, if preliminary, look at Rosetta’s comet. And what a wonderful and complex world it is.

Scientists have defined 19 regions on Comet 67P/Churyumov-Gerasimenko's nucleus grouped according to terrain. Each is named for an ancient Egytptian deity. Credits: ESA/Rosetta/MPS/OSIRIS Team/UPD/LAM/IAA/SSO /INTA/UPM/DASP/IDA — Scientists have defined 19 regions on Comet 67P/Churyumov-Gerasimenko’s nucleus according to terrain and named for Egyptian deities like Imhotep, Aten and Hathor. Credits: ESA/Rosetta/MPS/OSIRIS Team/UPD/LAM/IAA/SSO /INTA/UPM/DASP/IDA

Each of the papers describes a different aspect of the comet from the size and density of dust particles jetting from the nucleus, organic materials found on its surface and the diverse geology of its bizarre landscapes. Surprises include finding no firm evidence yet of ice on the comet’s nucleus. There’s no question water and other ices compose much of 67P’s 10 billion ton mass, but much of it’s buried under a thick layer of dust.

Despite its solid appearance, 67P is highly porous with a density similar to wood or cork and orbited by a cloud of approximately 100,000 “grains” of material larger than 2 inches (5 cm) across stranded there after the comet’s previous perihelion passage. Thousands of tiny comet-lets!
Continue reading “Latest Research Reveals a Bizarre and Vibrant Rosetta’s Comet”

January 24, 2015December 23, 2015 by Tim Reyes

There’s a Crack Forming on Rosetta’s 67P. Is it Breaking Up?

A Fissure spanning over 100 meters across the neck of Rosetta's comet 67P raises the question of if or when will the comet breakup. The fissure is part of released studies by Rosetta scientists in the Journal Science (Image Credits: ESA/Rosetta, Illustration, T.Reyes)

Not all comets break up as they vent and age, but for Rosetta’s comet 67P, the Rubber Duckie comet, a crack in the neck raises concerns. Some comets may just fizzle and uniformly expel their volatiles throughout their surfaces. They may become like puffballs, shrink some but remain intact.

Comet 67P is the other extreme. The expulsion of volatile material has led to a shape and a point of no return; it is destined to break in two. Songwriter Neil Sedaka exclaimed, “Breaking Up is Hard to Do,” but for comets this may be the norm. The fissure is part of the analysis in a new set of science papers published this week.

Top left: The Hathor cliff face is to the right in this view. The aligned linear structures can be clearly seen. The smooth Hapi region is seen at the base of the Hathor cliff. Boulders are prevalent along the long axis of the Hapi region. Bottom left and right: Crack in the Hapi region. The left panel shows the crack (indicated by red arrows) extending across Hapi and beyond. The right panel shows the crack where it has left Hapi and is extending into Anuket, with Seth at the uppermost left and Hapi in the lower left. (Credit: ESA/Rosetta)

The images show a fissure spanning a few hundred meters across the neck of the two lobe comet. The fissure is just one of the many incredible features on Comet 67P and is reported in research articles released in the January 22, 2015, edition of the journal Science.

What it means is not certain, but Rosetta team scientists have stated that flexing of the comet might be causing the fissure. As the comet approaches the Sun, the solar radiation is raising the temperature of the surface material. Like all materials, the comet’s will expand and contract with temperature. And diurnal (daily) changes in the tidal forces from the Sun is a factor, too.

An image sequence from the Navcam of the Rosetta spacecraft (right) is shown beside a simulation. Further work on the interaction of comets with solar radiation will include computer models that utilize Rosetta data to reveal how comet nuclei evolve over time – over many orbits of the Sun- and break up. Peanut, rubber-duck, potatoes or just round-shaped comet nuclei likely result from combinations of rotation, changes in rotation, spin rate, composition and internal structure, as a nucleus interacts with the Sun over many orbits. (Credits: ESA/Rosetta, Illustration – J.Schmidt)

The crack, or fissure, could spell the beginning of the end for comet 67P/Churyumov–Gerasimenko. It is located in the neck area, in the region named Hapi, between the two lobes that make 67P appear so much like a Rubber Duck from a distance. The fissure could represent a focal point of many properties and forces at work, such as the rotation rate and axis – basically head over heels of the comet. The fissure lies in the most active area at present, and possibly the most active area overall. Though the Hapi region appears to receive nearly constant sunlight, at this time, Rosetta measurements (below) show otherwise – receiving 15% less sunlight than elsewhere.

Left: A map looking at the northern (right-hand rule, positive) pole of 67P showing the total energy received from the Sun per rotation on 6 August 2014. The base of the neck (Hapi) receives ~15% less energy than the most illuminated region, 3.5 × 106 J m-2 (per rotation). If self-heating were not included, the base of the neck would receive ~30% less total energy. Right: Similar to the left panel but showing total energy received over an entire orbital period in J m-2 (per orbit). (Credit:ESA/Journal Science Article, Figure 5) — Left: A map looking at the northern (right-hand rule, positive,) pole of 67P showing the total energy received from the Sun per rotation on 6 August 2014. The base of the neck (Hapi) receives ~15% less energy than the most illuminated region, 3.5 × 106 J m-2 (per rotation). If self-heating were not included, the base of the neck would receive ~30% less total energy. Right: Similar to the left panel but showing total energy received over an entire orbital period in J m-2 (per orbit). (Credit:ESA/Journal Science Article, Figure 5)

Sunlight and heating are major factors and the neck likely experiences the greatest mechanical stresses – internal torques – from heating or tidal forces from the sun as it rotates and approaches perihelion. Rosetta scientists are still not certain whether 67P is two bodies in contact – a contact binary – or a shape that formed from material expelled about the neck area leading to its narrowing.

Fragmentation of comets is common. Many sungrazers are broken up by thermal and tidal stresses during their perihelions. At top, an image of the comet Shoemaker-Levy 9 (May 1994) after a close approach with Jupiter which tore the comet into numerous fragments. An image taken by Andrew Catsaitis of components B and C of Comet 73P/Schwassmann–Wachmann 3 as seen together on 31 May 2006 (Credit: NASA/HST, Wikipedia, A.Catsaitis) — Fragmentation of comets is common. Many sungrazers are broken up by thermal and tidal stresses during their perihelions. At top, an image of the comet Shoemaker-Levy 9 (May 1994) after a close approach with Jupiter which tore the comet into numerous fragments. An image taken by Andrew Catsaitis of components B and C of Comet 73P/Schwassmann–Wachmann 3 as seen together on 31 May 2006 (Credit: NASA/HST, Wikipedia, A. Catsaitis)

The Philae lander’s MUPUS thermal sensor measured a temperature of –153°C (–243°F) at the landing site, while VIRTIS, an instrument on the primary spacecraft Rosetta, has measured -70°C (-94°F) at present. These temperatures will rise as perihelion is reached on August 13, 2015, at a distance of 1.2432 A.U. (24% further from the Sun than Earth). At present – January 23rd – 67P is 2.486 A.U. from the Sun (2 1/2 times farther from the Sun than Earth). While not a close approach to the Sun for a comet, the Solar radiation intensity will increase by 4 times between the present (January 2014) and perihelion in August.

Hubble capture a sequence of images of the comet 73P/Schwassman-Wachmann 3. The comet fragmented and like 73P, Rosetta's 67P will likely breakup some day in two majore fragments with debris spreading out as in these images. The Solar wind pressure as well as any explosive force from the breakup causes the comet fragments to slowly disperse but altogether remain effectively in the same orbit. (Image Credit: NASA/Hubble) — Hubble captured a sequence of images of the comet 73P/Schwassman-Wachmann 3. The comet fragmented, and like 73P, Rosetta’s 67P will likely break some day into two major fragments with debris spreading out as in these images. The Solar wind pressure, as well as any explosive force from the break up, will cause the comet fragments to slowly disperse but effectively remain in the same orbit. (Image Credit: NASA/Hubble)

Stresses due to temperature changes from diurnal variations, the changing Sun angle during perihelion approach, from loss of material, and finally from changes in the tidal forces on a daily basis (12.4043 hours) may lead to changes in the fissure causing it to possibly widen or increase in length. Rosetta will continue escorting the comet and delivering images of the whole surface that will give Rosetta scientists the observations and measurements to determine 67P/Churyumov–Gerasimenko’s condition now and its fate in the longer term.

The fissure is not a very recent event. Universe Today's Bob King published an earlier image in his blog in September and added a question to illustrate. Whether the crack has widen since this time is not certain. (Image Credit: ESA, Illustration, Bob King) — The fissure is not a very recent event. Universe Today’s Bob King published an earlier image in his blog in September and added a question to illustrate. Whether the crack has widened since that time is not certain. (Image Credit: ESA, Illustration, Bob King)

Stay tuned for a forthcoming article from UT’s writer Bob King about numerous Rosetta mission scientific findings published this week in the journal Science.

Reference:

The morphological diversity of comet 67P/Churyumov-Gerasimenko

On the nucleus structure and activity of comet 67P/Churyumov-Gerasimenko

January 23, 2015December 23, 2015 by Elizabeth Howell

What Is The Difference Between the Geocentric and Heliocentric Models of the Solar System?

What does our Solar System really look like? If we were to somehow fly ourselves above the plane where the Sun and the planets are, what would we see in the center of the Solar System? The answer took a while for astronomers to figure out, leading to a debate between what is known as the geocentric (Earth-centered) model and the heliocentric (Sun-centered model).

The ancients understood that there were certain bright points that would appear to move among the background stars. While who exactly discovered the “naked-eye” planets (the planets you can see without a telescope) is lost in antiquity, we do know that cultures all over the world spotted them.

The ancient Greeks, for example, considered the planets to include Mercury, Venus, Mars, Jupiter and Saturn — as well as the Moon and the Sun. The Earth was in the center of it all (geocentric), with these planets revolving around it. So important did this become in culture that the days of the week were named after the gods, represented by these seven moving points of light.

All the same, not every Greek believed that the Earth was in the middle. Aristarchus of Samos, according to NASA, was the first known person to say that the Sun was in the center of the universe. He proposed this in the third century BCE. The idea never really caught on, and lay dormant (as far as we can tell) for several centuries.

Earth is at the center of this model of the universe created by Bartolomeu Velho, a Portuguese cartographer, in 1568. Credit: NASA/Bibliothèque Nationale, Paris

Because European scholars relied on Greek sources for their education, for centuries most people followed the teachings of Aristotle and Ptolemy, according to the Galileo Project at Rice University. But there were some things that didn’t make sense. For example, Mars occasionally appeared to move backward with respect to the stars before moving forward again. Ptolemy and others explained this using a system called epicycles, which had the planets moving in little circles within their greater orbits.

But by the fifteen and sixteenth centuries, astronomers in Europe were facing other problems, the project added. Eclipse tables were becoming inaccurate, sailors needed to keep track of their position when sailing out of sight of land (which led to a new method to measure longitude, based partly on accurate timepieces), and the calendar dating from the time of Julius Caesar (44 BCE) no longer was accurate in describing the equinox — a problem for officials concerned with the timing of religious holidays, primarily Easter. (The timing problem was later solved by resetting the calendar and instituting more scientifically rigorous leap years.)

While two 15th-century astronomers (Georg Peurbach and Johannes Regiomontanus) had already consulted the Greek texts for scientific errors, the project continued, it was Nicolaus Copernicus who took that understanding and applied it to astronomy. His observations would revolutionize our thinking of the world.

Retrograde motion of Mars. Image credit: NASA

Published in 1543, Copernicus’ De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Bodies) outlined the heliocentric universe similar to what we know today. Among his ideas, according to Encyclopedia Britannica, was that the planets’ orbits should be plotted with respect to the “fixed point” Sun, that the Earth itself is a planet that turns on an axis, and that when the axis changes directions with respect to the stars, this causes the North Pole star to change over time (which is now known as the precession of the equinoxes.)

Putting the Sun at the center of our Solar System, other astronomers began to realize, simplified the orbits for the planets. And it helped explain what was so weird about Mars. The reason it backs up in the sky is the Earth has a smaller orbit than Mars. When Earth passes by Mars in its orbit, the planet appears to go backwards. Then when Earth finishes the pass, Mars appears to move forwards again.

Other supports for heliocentrism began to emerge as well. Johannes Kepler’s rules of motions of the planets (based on work from him and Tycho Brahe) are based on the heliocentric model. And in Isaac Newton’s Principia, the scientist described how the motions happen: a force called gravity, which appears to be “inversely proportional to the square of the distance between objects”, according to the University of Wisconsin-Madison.

Artist's conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech — Artist’s conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech

Newton’s gravity theory was later supplanted by that of Albert Einstein, who in the early 20th century proposed that gravity is instead a warping of space-time by massive objects. That said, heliocentric calculations guide spacecraft in their orbits today and the model is the best way to describe how the Sun, planets and other objects move.

Universe Today has articles on both the heliocentric model and the geocentric model, and Astronomy Cast has an episode on the center of the universe.

January 22, 2015December 23, 2015 by Vanessa Janek

The Entire Milky Way Might Be a Huge Wormhole That’s Stable and Navigable

Artist rendering of a wormhole connecting two galaxies. Credit: Davide and Paolo Salucci

Our very own Milky Way could be home to a giant tunnel in spacetime.

At least, that’s what the authors of a new study have proposed. According to the team, a collaboration between Indian, Italian, and North American researchers at the International School for Advanced Studies (SISSA) in Italy, the central halo of our galaxy may harbor enough dark matter to support the creation and sustenance of a “stable and navigable” shortcut to a distant region of spacetime – a phenomenon known as a wormhole.

Wormholes were first conceptualized by Albert Einstein and Nathan Rosen in 1935. Far from being fodder for science fiction, the two scientists instead proposed their idea as a way to get around the idea of black hole singularities. Rather than creating a knot of infinite density, Einstein and Rosen thought, the hefty energy inherent in such a massive body would distort spacetime to such an extent that it bent over on itself, allowing a bridge to form between two distant areas of the Universe. Alas, these wormholes would be extremely unstable and would require enormous amounts of “negative energy” to remain open.

Wormhole diagram. Image credit: NASA — A graphic of the structure of a theorized wormhole (NASA)

But according to the team at SISSA, large amounts of dark matter could provide this fuel. Using a model of dark matter’s abundance that is based on the rotation curves of other spiral galaxies, the researchers found that the distribution of dark matter in the Milky Way produced solutions in general relativity that would, theoretically, allow a stable wormhole to arise.

Paulo Salucci, an astrophysicist on the the team from SISSA, explained: “If we combine the map of the dark matter in the Milky Way with the most recent Big Bang model to explain the universe and we hypothesise the existence of space-time tunnels, what we get is that our galaxy could really contain one of these tunnels, and that the tunnel could even be the size of the galaxy itself.” He continued, “But there’s more. We could even travel through this tunnel, since, based on our calculations, it could be navigable. Just like the one we’ve all seen in the recent film Interstellar.”

Of course, Salucci and the other researchers were working on this project long before Interstellar was released, but their result does lend some theoretical support to the ideas in the film – ideas that were also fact-tested and revised by physics guru Kip Thorne of Caltech.

The authors believe that their result reinforces the importance of discerning the true nature of dark matter. According to Salucci, “Dark matter may be ‘another dimension’, perhaps even a major galactic transport system. In any case, we really need to start asking ourselves what it is”.

It is important to understand that this is purely a mathematical result. Indeed, such a wormhole may be theroretically possible… but that doesn’t mean it’s probable. Salucci ventured, “Obviously we’re not claiming that our galaxy is definitely a wormhole, but simply that, according to theoretical models, this hypothesis is a possibility.”

The researchers went on to explain that their idea could be tested experimentally by comparing our own Milky Way, a spiral galaxy, with a nearby galaxy of a different type. By comparing the dark matter distributions between the two galaxies, scientists would potentially be able to use general relativity to probe differences in their spacetime dynamics.

Realistically, the technology that would allow researchers to do that is a long way off. But never fear, science (and scifi) fans – you can still check out the team’s wormhole simulation in the animation below, watch the movie if you haven’t already, and/or get your hands on a copy of Kip Thorne’s book, The Science of Interstellar.

The team’s research was published in the November 2014 issue of Annals of Physics. A pre-print of the paper is available here.

January 22, 2015December 23, 2015 by Elizabeth Howell

10 Amazing Facts About Black Holes

An artists illustration of the central engine of a Quasar. These "Quasi-stellar Objects" QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA)

Imagine matter packed so densely that nothing can escape. Not a moon, not a planet and not even light. That’s what black holes are — a spot where gravity’s pull is huge, ending up being dangerous for anything that accidentally strays by. But how did black holes come to be, and why are they important? Below we have 10 facts about black holes — just a few tidbits about these fascinating objects.

Fact 1: You can’t directly see a black hole.

Because a black hole is indeed “black” — no light can escape from it — it’s impossible for us to sense the hole directly through our instruments, no matter what kind of electromagnetic radiation you use (light, X-rays, whatever.) The key is to look at the hole’s effects on the nearby environment, points out NASA. Say a star happens to get too close to the black hole, for example. The black hole naturally pulls on the star and rips it to shreds. When the matter from the star begins to bleed toward the black hole, it gets faster, gets hotter and glows brightly in X-rays.

Fact 2: Look out! Our Milky Way likely has a black hole.

A natural next question is given how dangerous a black hole is, is Earth in any imminent danger of getting swallowed? The answer is no, astronomers say, although there is probably a huge supermassive black hole lurking in the middle of our galaxy. Luckily, we’re nowhere near this monster — we are about two-thirds of the way out from the center, relative to the rest of our galaxy — but we can certainly observe its effects from afar. For example: the European Space Agency says it’s four million times more massive than our Sun, and that it’s surrounded by surprisingly hot gas.

*Sagittarius A in infrared (red and yellow, from the Hubble Space Telescope) and X-ray (blue, from the Chandra space telescope). Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI*

Fact 3: Dying stars create stellar black holes.

Say you have a star that’s about 20 times more massive than the Sun. Our Sun is going to end its life quietly; when its nuclear fuel burns out, it’ll slowly fade into a white dwarf. That’s not the case for far more massive stars. When those monsters run out of fuel, gravity will overwhelm the natural pressure the star maintains to keep its shape stable. When the pressure from nuclear reactions collapses, according to the Space Telescope Science Institute, gravity violently overwhelms and collapses the core and other layers are flung into space. This is called a supernova. The remaining core collapses into a singularity — a spot of infinite density and almost no volume. That’s another name for a black hole.

Fact 4: Black holes come in a range of sizes.

There are at least three types of black holes, NASA says, ranging from relative squeakers to those that dominate a galaxy’s center. Primordial black holes are the smallest kinds, and range in size from one atom’s size to a mountain’s mass. Stellar black holes, the most common type, are up to 20 times more massive than our own Sun and are likely sprinkled in the dozens within the Milky Way. And then there are the gargantuan ones in the centers of galaxies, called “supermassive black holes.” They’re each more than one million times more massive than the Sun. How these beasts formed is still being examined.

A binary black hole system, viewed from above. Image Credit: Bohn et al. (see http://arxiv.org/abs/1410.7775) — *A binary black hole system, viewed from above. Credit: Bohn et al. (see http://arxiv.org/abs/1410.7775)*

Fact 5: Weird time stuff happens around black holes.

This is best illustrated by one person (call them Unlucky) falling into a black hole while another person (call them Lucky) watches. From Lucky’s perspective, Unlucky’s time clock appears to be ticking slower and slower. This is in accordance with Einstein’s theory of general relativity, which (simply put) says that time is affected by how fast you go, when you’re at extreme speeds close to light. The black hole warps time and space so much that Unlucky’s time appears to be running slower. From Unlucky’s perspective, however, their clock is running normally and Lucky’s is running fast.

Fact 6: The first black hole wasn’t discovered until X-ray astronomy was used.

Cygnus X-1 was first found during balloon flights in the 1960s, but wasn’t identified as a black hole for about another decade. According to NASA, the black hole is 10 times more massive to the Sun. Nearby is a blue supergiant star that is about 20 times more massive than the Sun, which is bleeding due to the black hole and creating X-ray emissions.

Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. (NASA/CXC/M.Weiss) — *Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. Credit: NASA/CXC/M.Weiss*

Fact 7: The nearest black hole is likely not 1,600 light-years away.

An erroneous measurement of V4641 Sagitarii led to a slew of news reports a few years back saying that the nearest black hole to Earth is astoundingly close, just 1,600 light-years away. Not close enough to be considered dangerous, but way closer than thought. Further research, however, shows that the black hole is likely further away than that. Looking at the rotation of its companion star, among other factors, yielded a 2014 result of more than 20,000 light years.

Fact 8: We aren’t sure if wormholes exist.

A popular science-fiction topic concerns what happens if somebody falls into a black hole. Some people believe these objects are a sort of wormhole to other parts of the Universe, making faster-than-light travel possible. But as this Smithsonian Magazine article points out, anything is possible since we still have a lot to figure out about physics. “Since we do not yet have a theory that reliably unifies general relativity with quantum mechanics, we do not know of the entire zoo of possible spacetime structures that could accommodate wormholes,” said Abi Loeb, who is with the Harvard-Smithsonian Center for Astrophysics.

*Diagram of a wormhole, or theoretical shortcut path between two locations in the universe. Credit: Wikipedia*

Fact 9: Black holes are only dangerous if you get too close.

Like creatures behind a cage, it’s okay to observe a black hole if you stay away from its event horizon — think of it like the gravitational field of a planet. This zone is the point of no return, when you’re too close for any hope of rescue. But you can safely observe the black hole from outside of this arena. By extension, this means it’s likely impossible for a black hole to swallow up everything in the Universe (barring some sort of major revision to physics or understanding of our Cosmos, of course.)

Fact 10: Black holes are used all the time in science fiction.

There are so many films and movies using black holes, for example, that it’s impossible to list them all. Interstellar‘s journeys through the universe includes a close-up look at a black hole. Event Horizon explores the phenomenon of artificial black holes — something that is also discussed in the Star Trek universe. Black holes are also talked about in Battlestar: Galactica, Stargate: SG1 and many, many other space shows.

Here on Universe Today we have a great article about a practical use for black holes: as spacecraft engines. No one can get to a black hole without space travel. Astronomy Cast offers a good episode about interstellar travel.