I Know Why the Black Hole Sings

July 08, 2009

Black Hole Week is still going strong here at Twisted Physics. There's no end to surprising facts about these enigmatic objects. One of my favorite black hole discoveries of the last few years was the 2003 detection of a "singing black hole" at the center of a galaxy in the Perseus Cluster, some 250 million light years from Earth. It's not actually trilling its way through a famous operatic aria like "Nessun Dorma" -- Luciano Pavarotti's reputation is secure -- and it only sings one note: B flat. But it is the lowest possible B flat ever detected.

The Cambridge University scientists used the middle C note on a piano keyboard as a reference point when determining where the droning note emitted by the black hole would fall on the musical scale. On a keyboard, the B Flat nearest middle C is 1-1/2 steps away.

The black hole's B Flat, however, is a whopping 57 octaves below middle C -- one million, billion times lower than what the human ear can detect. That gives the sound waves a frequency of 10 million years, compared to 1/20th of a second.

They are the result of the sound waves, transmitted through the bits of dust and gas that make up the interstellar medium. Chandra saw lots of concentric ripples in the interstellar medium -- ripples the size of 30,000 light years. The actual ripples are caused by gravitational effects from all those galaxies clumped together in the Perseus Cluster. The black hole pulls matter in, but in the process jets of material shoot out around it, creating pressure waves. And to scientists, pressure waves are just sound waves. Anyway, it was this X-ray radiation that NASA's Chandra X-Ray Observatory detected in 2003, providing indirect evidence of a "singing" black hole.

Because they carry acoustical energy, those sound waves keep the gas dispersed throughout the cluster warmer than it would otherwise be. It's not just a bizarre acoustical curiosity, either: those warmer temperatures regulate the rate at which new stars form, so the sound waves could prove to be critical to our understanding of how the universe's structure evolves.

Our musical black hole in the Perseus cluster might be a one-note wonder, but Pavarotti never promised to unlock the secrets of galaxy formation. We're just sayin'....

Image: Sound waves from a black hole in the Perseus Cluster. Source: NASA/Chandra.

The Haunting of HDF 130

Some 10 billion light years away is a mysterious "X ray source" that dates back to a mere 3 billion years after the Big Bang -- right when lots of galaxies and blacks were forming. It seems to be a kind of "cosmic ghost" lurking around a distant black hole, according to scientists with NASA's Chandra X-Ray Observatory mission. We're not talking "ghost" as in that 1990s Patrick Swayze movie; this is lingering evidence of a huge eruption from a black hole.

That's what Cambridge University's Andy Fabian thinks, anyway. "We'd seen this fuzzy object a few years ago but didn't realize until now that we were seeing a ghost," he says. "It's not out there to haunt us, rather it's telling us something -- in this case, what was happening in this galaxy billions of years ago."

Sounds kind of like an "actual" (and I use that term loosely) ghost to me -- they're always trying to solve their own murders or reveal secrets of the past. In this case, the "ghost" is the X-ray remnant "afterglow" of a power explosion from the central black hole -- so big, it would have been the equivalent of a billion supernovae. That is one violent event.

This kind of outburst produces a huge amount of radio and X-ray radiation that usually dies down after a few million years. So why are we seeing this ghostly X-ray remnant? Fabian explains that the cosmic microwave background is to blame -- another glowing artifact, this time from the actual Big Bang. Less energetic electrons can still produce x-rays, it seems, because they keep colliding with photons in the CMB. This gives them a boost of extra energy so they emit faintly in the X-ray regime of the spectrum. The result is a lingering X-ray source that can last as long as 30 million years after the initial radiation has died away.

That's not all: HDF 130 might not be the only object being haunted. Fabian and his co-author, Caitlin Case, figure that the night sky is actually filled with these sorts of "ghosts"; black holes apparently erupt more often than you might think. So long as they're the "good" kind of "ghost" that helps us solve the mysteries of our early universe, that's probably okay.

Image: HDF 130 as seen in the Chandra Deep Field North, one of the deepest X-ray images ever taken. NASA/Chandra X-Ray Observatory

Under a Dark Star

July 07, 2009

Welcome to Black Hole Week at Twisted Physics: Part Deux. We think of black holes as a 20th century invention, dating back to 1916, when Einstein published his theory of general relativity and fellow physicist Karl Schwarzschild used those equations to envision spherical section of spacetime so badly warped around a concentrated mass that it is invisible to the outside world. But the true "father" of the black hole concept was a humble 18th century English rector named John Michell -- a man so far ahead of his scientific contemporaries that his ideas languished in obscurity, until they were re-invented more than a century later.

Born in 1724, Michell attended Cambridge University and wound up teaching there for a time, before becoming rector of Thornhill, near the town of Leeds. He is described somewhat unflatteringly in contemporary accounts as "a little short man, of black complexion, and fat," who was nonetheless "esteemed a very ingenious Man, and an excellent Philosopher." For a small-town rector, he had some pretty impressive scientific connections: Benjamin Franklin, Joseph Priestley and Henry Cavendish all visited him at some point in his career.

Michell's research interests were all over the map. He started out looking into magnetism, then made a few waves after the big Lisbon earthquake of 1755, proposing that earthquakes propagate as waves through solid earth -- thereby helping establish the field of seismology.

He conceived and designed the experimental apparatus later used by Cavendish to measure the force of gravity between masses in the laboratory to get the first accurate value for the gravitational constant ("G"). And he was the first to apply statistical methods to astronomy, studying how stars were distributed in the night sky and arguing that there were far more "pairs" or groups or stars than would happen with random alignments. His analysis provided the first evidence for binary stars, and star clusters.

But it was a paper Michell wrote in 1783 that proved the most revolutionary. He didn't set out to "invent" black holes; he was just casting about for a handy method to figure out the mass of a star.

This was before scientists knew that light was both particle and wave, and Michell sided with the pro-particle Newton. And since light was made of particles, he figured that when they were emitted by a star, that star's gravitational pull would reduce their speed -- much like what happens when you toss an apple into the air. He thought he could measure how much the speed of light was reduced and from that, calculate the mass of a star.

It was a sensible enough scheme: Ole Roemer had measured the speed of light the century before, so Michell had a ballpark figure with which to work. He also understood the concept of "escape velocity" -- namely, any light particle must move faster than a certain critical speed in order to escape from a star's gravitational pull. And that critical speed would be determined by the mass and size of the star.

Here's where Michell found himself pondering an intriguing "what if?" scenario: what would happen if a star was so massive, and its gravity so strong, that the escape velocity was greater than the speed of light? Well, what happens when you throw an apple into the air without sufficient velocity to escape the Earth's gravity? It falls back down to Earth. Michell figured the same thing would happen to particles of light emitted by a super-massive star more than 500 times the mass of the sun: it would fall back to the surface, rendering that star invisible to astronomers.

Michell even thought it might be possible to indirectly detect such "dark stars" if they had a luminou "twin" circling them -- a binary star system -- making him doubly prescient. It's one of several different methods modern astronomers use to infer the existence of black holes.

Today we define black holes as volumes of space in which gravity is so strong, not even light can escape. It might be said that John Michell, that short, fat rector, was born under a dark star. He never achieved sufficient escape velocity for his ideas to break out of Thornhill. He died in quiet obscurity, and his notion of a "dark star" -- that Newtonian precursor to our modern notion of a black hole -- was forgotten until his writings re-surfaced in he 1970s. Consider it a form of conceptual Hawking radiation: eventually, his ideas found their way into the light.

Image: Title and excerpt from Michell's 1783 paper in which he first described the concept of a "dark star." Source: Philosophical Transactions of the Royal Society of London, Vol. 74, p.35, 1783.

Black Holes Gone Rogue

It's Black Hole week here at Twisted Physics, primarily because my fodder file is choked to the brim with various collected items related to these gravitational bad boys of physics. How bad are they? Michael Jackson "Beat It" bad. In fact, a couple of months ago, scientists at the Harvard-Smithsonian Center for Astrophysics warned of rogue black holes rum amok in the Milky Way, ready to gobble up any random bits of matter that stumble into their path, just like the army of zombies in "Thriller."

Fortunately, our pretty blue planet doesn't hang out in those sorts of neighborhoods -- ours is more of a gated community type of planet, where the neighbors keep the lawns well-tended and everyone's kids attend private school. The closest rogue black hole should be several thousand light years away. And it's just a theoretical prediction right now. So these objects are mostly of interest to astrophysicists who like to walk on the wild side of their research now and then. Rogue black holes are remnants from the days when the early universe was just starting to form galaxies, like our Milky Way, so studying them could provide clues to the mechanisms underlying galaxy formation.

HSCfA's Ryan O'Leary and Avi Loeb say that rogue black holes probably started out with some small-time, juvie stuff: individual black holes lurking at the centers of tiny galaxies with very little mass, waiting for trouble to find them. Turf wars were almost inevitable in the roiling days of the early universe: these tiny galaxies would occasionally collide (rumble!), and every time this happened, the black holes at the center of each would join forces and merge to form a gang single "relic" black hole.

Where might we find these rogue black holes today? Probably in the outer reaches of the Milky Way. That's because when two black holes merges, they would emit a powerful kick of gravitational radiation and recoil in response. It would be strong enough to propel the new relic black hole to the outer edge of the galaxy, but not strong enough to leave the state completely. They should still be lurking there: hundreds of them, each with a mass ranging from 1000 to 1000,000 times the mass of our sun.

Not that we'd be able to see them. They're more like rogue ninjas in that respect, only visible in the act of consuming -- or, as astrophysicists call it, "accreting" -- matter. But Loeb and O'Leary think that there might be another telltale sign of a rogue black hole's existence: highly compact star clusters. Apparently rogue black holes travel with a posse of hangers-on. When the black hole recoils out of the dwarf galaxy, it takes a small retinue of stars with it, just those nearest to the Great Gobbler.

Such a cluster would be small enough, and dense enough, that it might look to us like a single star. Astronomers would need to study the spectrum of stars in existing sky surveys carefully to determine if there were one, or multiple stars. Either way, "The surrounding star cluster acts much like a lighthouse that pinpoints a dangerous reef," says O'Leary. We can find a rogue black hole by the dense company it keeps.

Image: David Aguilar, Harvard-Smithsonian Center for Astrophysics.

Carnival of Space #109

June 29, 2009

Welcome to Carnival of Space #109!

First off, Starts With a Bang continues the countdown on his ongoing list of great space-y scientists over the last 100 years; this week's installment names Fred Hoyle as "scientist of the 1950s." Hoyle won the Nobel Prize for his work in nucleosynthesis, yet steadfastly rejected the Big Bang theory even as it gained ground among his colleagues -- and we mean the actual theory, people, not the popular sitcom of the same name.

In other history news, Beyond Apollo delves into NASA's historical archives and finds out that yes, the agency had a backup plan in the 1960s, just in case the Saturn V rocket or Apollo spacecraft got stuck in development. We now know Plan B proved unnecessary, but it's a fascinating glimpse into the lesser-known aspects of NASA history. Meanwhile, Cumbrian Sky bemoans the dearth of photgraphic and video documentation of the Apollo 11 moon landing, pronouncing this lack a major FAIL.

Over at AstroEngine, Ian asks a burning question: How do you directly observe a black hole when it's 26,000 light years away. The answer involves an array of telescopes with "very large baselines," apparently. For details on this "Event Horizon Telescope," check out the full post. Meanwhile, Olaf of Cosmic Web revisits a famous telescope of yesteryear -- Lord Rosse's aptly named "Leviathan of Parsontown" -- which was the first to resolve the spiral structure of the so-called Whirlpool Galaxy (M51).

Our favorite Bad Astronomer, Phil Plait, reports on conflicting findings regarding Saturn: one group reports the presence of sodium in the particles that make up the outermost ring, whereas another team reports a lack of sodium in the geysers of water spewing from the icy moon Enceladus. "Two observations, two good teams, two very different conclusions. That's what it's like on the cutting edge..."

Over at Mang's Bat Page -- I learned this morning that Mang is the name of a bat in The Jungle Book -- there's a fascinating post about the Incredible Shrinking Planet, a.k.a., Mars, debunking the latest rash of emails claiming the Red Planet will appear as large as the full moon.

How did you spend your summer solstice? Ian of Astroblog spent it showing Saturn to a group of guests at a rooftop garden party, complete with a capella vocals. And then they sacrified a goat to the God of the Underworld (okay, not really)...

My pop-culture-loving heart warmed to read Out of the Cradle's killer list of B-movies featuring forward-looking visions of the Moon -- many of which are only available on VHS, having never merited a wide enough audience to justify a DVD release. And for all you hard-core aspiring lunar colonists, Potentia Tenebras Repellendi has created a "fan map" of the moon. On hand with a proposal to foment creative new design ideas for spacecraft of the future -- so we can all travel to the moon and beyond in style -- is John of Open Nasa. He proposes a Wikimedia project to harness some of the knowledge and expertise roiling around out there.

Universe Today has a tantalizing story of possibly solving the Tunguska mystery; a comet may be to blame! Meanwhile, the latest Cheap Astronomy podcast gives an overview of recent theories about the dinosaur extinction 65 million years ago, finding "more smoking guns than a Dallas motorcase." We're just saying, there may have been a second asteroid hanging out on the grassy knoll...

There's good news and bad news on the funding front. First, the good news, which comes to us via Next Big Future: the Canadian government has awarded $13.9 million (in Canadian currency) to General Fusion to demonstrate a workable nuclear fusion power source. Now, the bad news, via Centauri Dreams: the TESS mission -- intended to single out bright nearby stars for an exoplanet search -- didn't make NASA's latest cut for funding. Check out the post to find out which missions were picked instead.

TESS might be grounded in its search for exoplanets, but Bruce at 21st Century Waves reports that "Caltech scientists have recently shown that the presence of biology on a terrestrial planet acts naturally to more than double the lifetime of the planet's biosphere." Bruce explains why this is important for the prospects of extraterrestrial life.

And finally, what carnival would be complete with Space Porn? Offering the prettiest space pictures this past week: Todd at Catholic Sensibility has some stunning images of shadows cast on the rings of Saturn during the planet's equinox. Enjoy!

Photos: (top) A sketch of M51, the "Whirlpool Galaxy." (bottom) Historical photo of aftermath of Tunguska event.

Digitizing von Braun

June 28, 2009

Via Wired comes news that NASA is asking the public for advice on how to best "analyze and electronically catalog a precious collection of notes that chronicle the early history of the human space flight program." The author of those notes? Rocketry pioneer Werner von Braun. The article quotes project manager Jason Crusan on why NASA deems this an important project: "It's first-hand insight on how management and engineering decisions were made on a real-time basis."

The young von Braun was enthralled by explosives and fireworks, to the great chagrin of his father, who considered his son a juvenile delinquent. As a teenager, he strapped six skyrockets to a red toy wagon and set them off. The wagon traveled five blocks, streaming flames, before the rockets exploded, destroying the wagon, and von Braun was arrested.

Despite this inauspicious beginning, he went on to earn a PhD in physics in the late 1930s. Within two years he found himself heading Nazi Germany’s military rocket development program. He invented the V-2 ballistic missile, first launched on October 3, 1942. This would be the ancestor of practically every missile used today.

After Germany's defeat in 1945, von Braun and his entire team of rocket experts came to the US with all their plans and prototypes. But Von Braun had never wanted to build weapons; he dreamed of using rockets to travel into space. Long before his scientific career was launched, he had read a prophetic 1923 book entitled, The Rocket Into Interplanetary Space, by Romanian-born scientist Hermann Oberth, who in turn had been influenced as a boy by reading Jules Verne's sci-fi novel, From the Earth to the Moon.  Oberth devised the notion of using stages of rockets, jettisoning each section as its fuel was depleted, to maintain a big enough ratio between propellant and rocket mass so that the rocket could travel at sufficiently high speeds.

By 1960, von Braun got closer to his dream when he was appointed head of the Marshall Spaceflight Center, leading the development of the Saturn rocket project, and played a critical role in the early days of the Apollo program. He retied in 1972.

Through it all, he apparently kept copious notes, carefully typewritten with lots of scribbling of additional comments in the margins (see a sample here). NASA re-discovered those notes stashed away in boxes about six months ago, and would like to turn them into a useful database. You can find the official NASA request for information here. Feel free to weigh in with your ideas on format, indexing strategies and the like. NASA would love to hear from you -- by August 31.

"All You Need is the Rocket Experience..."

June 23, 2009

Next month marks the 40th anniversary of the Apollo 11 moon landing, when NASA astronauts Neil Armstrong and Buzz Aldrin boarded the lunar module and took one small step for man on the surface of the moon. There are lots of activities planned to commemorate this historic event, but Aldrin's taken a distinctly quirkier approach: he's made a hip-hop video with Snoop Dogg and Talib Kweli (of Black Star fame), with the proceeds going to benefit various space exploration foundations.

Even better, Funny or Die got into the act and made a tongue-firmly-in-cheek "Behind the Scenes" video about the making of "Rocket Experience," featuring numerous rappers giving Aldrin a few tips, and talking about the moon landing's impact on their lives. (Check out Snoop Dogg's lyrical rap tribute to Buzz at the very end.) Per Kweli: "Buzz Aldrin got his bars up!"

Making of Buzz Aldrin's Rocket Experience w/ Snoop Dogg and Talib Kweli from Buzz Aldrin

And now, for your listening pleasure, here's Buzz Aldrin -- a.k.a."Doc Rendezvous" -- in the final video cut for "Rocket Experience," directed by none other than McG (Terminator: Salvation):

Buzz Aldrin's Rocket Experience from Buzz Aldrin

World's First Weightless Wedding

June 22, 2009

Some kind of space history was made over the weekend, as NYC couple Erin Finnegan and Noah Fulmor exchanged wedding vows while in zero gravity aboard G-Force One -- affectionately known as "the vomit comet." The aircraft flew a series of 15 parabolas, resulting in five "weightless" intervals of 30 seconds. The quickie ceremony was performed during those intervals, with some room for second takes just in case, say, the bride or groom threw up.

At heart, the vomit comet is the world's most awesome roller coaster, taking such extreme lifts and dips in its parabolic trajectory that it can achieve a reasonably sustained freefall (about 20-30 seconds of freefall out of every 65 seconds). The ride starts with a steep, 45-degree climb, followed by a dip downward, during which those precious moments of weightlessness can be experienced.

Getting married in zero gravity does present some unique challenges to a wedding planner. Finnegan wore a specially designed gown with a tiered skirt designed to billow out in all directions -- with pants underneath so the bride need not worry about revealing her undergarments as she tumbled about for the full weightless experience. They couldn't get insurance for the wedding, although it will be legal, since the airpace over Cape Canaveral is still within the state of Florida's jurisdiction.

Chief among the obstacles was the exorbitant cost. I know weddings run up ridiculous tabs these days, but the bride and groom and their seven family members/guests forked over $5400 per person. (An anonymous soldier in Iraq paid for half the ticket for Finnegan's mom, who was understandbaly a bit sqeamish at both the price and the zero gravity .) They also had to cover the cost of an onboard photographer and videographer -- becuase this was definitely a wedding that cried out for photographic documentation.

Was it worth it? Probably -- that's certainly a wedding day one is unlikely to forget. And the happy couple have been space enthusiasts since they were kids; among other things, they hope their nuptials can raise awareness for the future of private space exploration. "We're saying, the future is going to be awesome," Fulmor told New Scientist. "The future is here if you want it. We're getting married in zero gravity!"

Mazel tov to Finnegan and Fulmor...

Twinkle, Twinkle, Neutron Star

June 16, 2009

Neutron stars are mysterious beasts. Sure, astrophysicists know they're the result of a massive star compressing during a supernova and collapsing in on itself. And they know it retains most of its angular momentum in the process, and has an incredibly high surface gravity. But they don't know what exactly the surface of a neutron star is made of, although it's clear that iron plays a role -- our instruments have detected the telltale spectral signature of iron in emissions from these objects. Nor is it clear whether the iron is in gaseous form, thereby forming a sort of "atmosphere," or whether it forms an ultra-hard solid crust.

A couple of weeks ago, a paper appeared on the arXiv with an intriguing means of telling the difference. Two Spanish scientists at the Universidad Complutense in Madrid conclude that if the iron in a neutron star is solid, it will form a rare and unusual crystal that is perfectly smooth and would envelop the entire star. And they've devised a method to test this by studying the surface of neutron stars using x-ray crystallography.

The idea is to look for binary neutron star systems: one "dead," with an iron crust, the other an x-ray pulsar. X-ray emissions from the pulsar should hit the surface of its partner, and those rays should be diffracted and thus detectable by our terrestrial instruments. Assuming they can find these sorts of couplings -- roughly 5% of neutron stars belong to binary star systems -- scientists could learn a great deal more about the structure and behavior of neutron stars.

There could be yet another means of studying the structure of neutron stars: observing the frequency spectra of stellar oscillations, more commonly known as "starquakes." There is actually a subfield known as asteroseismology, although it specializes in ordinary stars. Neutron stars also have these sorts of seismic events, in which the stiff surface crust ruptures much like terrestrial (tectonic) earthquakes. It happens because as a neutron star ages, its rotation gradually slows down, and its shape becomes more spherical through a series of stellar quakes.

Stellar quakes also cause neutron stars to flare brightly temporarily with so-called x-ray oscillations. Astrophysicists think this is because after the quake, the equatorial radius is slightly smaller; neutron stars spin and thus have angular momentum, which must be conserved. So the extra energy is released as x-rays.

That's bad news for x-ray satellites, since they are momentarily blinded by the light. But it's good news for the x-ray photons themselves, which finally have sufficient energy to overcome the star's immense surface gravity (about 10<11> times that of Earth) and escape. Sometimes photons need their freedom, too -- it's a big, big universe out there.

Photo:  An artists's concept of the 2004 occurence in which a neutron star underwent a "star quake", causing it to flare brightly, temporarily blinding all x-ray satellites in orbit. Source: NASA. Public domain.

Rare Isotope Rap

June 15, 2009

She's baaack! AlpineKat (a.k.a., Kate MacAlpine), that is, who gave us the Large Hadron Rap last year -- currently viewed by over 5 million people on YouTube, and still counting. This time, she busts a rhyme over the Facility for Rare Isotope Beams (FRIB), a new project of the DOE being bult at Michigan State University in East Lansing. MSU hosted an event this past week to celebrate the future of rare isotope research, and AlpineKat was on hand to debut her new rap in full HD version: three elevated screens 14 feet across, augmented by a cutting-edge sound system.

This is the way physics rap was meant to be experienced, I'm sure, although YouTube is still the best way to reach a massive audience. Here's what MacAlpine had to say last year in Symmetry Magazine:

I think rap is a good way to communicate. Rhyme has always helped embed words in my mind; hopefully science rap can help cement ideas in the minds of students and other interested people. “Nerdcore” has been on the Web for a while, fusing “nerdy” from the cultures of video games and hard science with the “hardcore” of rock and hip-hop.

Check out the cameo appearance of Brad Sherrill, chief scientist of FRIB and a distinguished professor of physics at MSU -- who has a little fun wagging his bushy eyebrows mischievously at the camera.

In the case of FRIB, there's precious little material on the Web that isn't either highly technical, or, well, exceedingly non-specific -- what is it about DOE Web copy that puts a reader to sleep faster than Proust's Remembrances of Things Past? But give them time: FRIB is a brand new facility, after all. AlpineKat's Rare Isotope Rap is a welcome summary of what the project is, how it works, and why we should care about studying rare isotopes.

Rare isotopes are short-lived nuclei not normally found on Earth, and as AlpineKat raps, scientists still don't understand why some isotopes are stable while others decay. Investigating this myster could reveal clues about the life cycles of stars and the birth of the elements -- most of the heavier elements (everything except hydrogen, helium, and a bit of lithium and other light atoms) are the result of supernova explosions). Some of these rare isotopes could also lead to better diagnosis and treatment of human diseases, so it's not just all about esoteric, space-age science.

People keep asking MacAlpine about possible record deals, and she's pretty realistic about those prospects: "I don't think that'll be happening any time soon." And that's just fine by me. The music industry's loss is physics rap's gain. Five million YouTube viewers blows most record sales out of the water.