Ivan Semeniuk’s Embedded Universe

Near Earth asteroids, like Itokawa (imaged here by Japan's Hayabusa mission) may be nothing more than loose rubble piles that can be severely shaken up by close encounters with Earth. (ISAS, JAXA)

Late one night a couple of years ago I found myself in the Green Building, the signature high rise that towers over the MIT campus––where I was watching asteroids with Rick Binzel.   

Binzel is a consummate asteroid lover.  He has studied them for years with a passion that reminds us there are many more worlds in the solar system than the eight or nine planets whose names we learned in elementary school.

The asteroids he showed me that night were nothing more than dim blips on a video screen.  Our view was a live connection to NASA’s Infrared Telescope Facility on Mauna Kea in Hawaii, which Binzel uses remotely to study Near Earth Asteroids (NEA’s), small asteroids that pass near—sometimes uncomfortably near—to our planet. There are thousands of NEAs out there, silently parading by in the shadows. Binzel is motivated to study these wayward drifters because he finds their many puzzles and quirks utterly fascinating. They also have the potential to dramatically disrupt the course of life on Earth.

Now it appears the reverse is also true: According to the data Binzel has patiently gathered, Earth can dramatically disrupt asteroids, even causing them to change colour if they get too near. Furthermore, this intriguing result helps resolve a decades-long meteorite mystery. Continue reading →

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The spiral density waves generated by a simulated proto-Earth in the surrounding simulated gas will eventually spell simulated disaster for our digital counterparts. How did the real Earth avoid the same fate? (image courtesy Wilhelm Kley, University of Tübingen)

You may think you have a hard job, but imagine this item on your to-do list:  saving Earth from non-existence.  It sounds like a task worthy of Superman but it has fallen instead to computational astrophysicists like Mordecai-Mark Mac Low of the American Museum of Natural History to make sure our planet is spared oblivion—or at least virtual oblivion in numerical simulations.

 Mac Low’s challenge stems from a key mystery in our current picture of how planets are formed.   It’s long been thought that Earth coalesced from a gaseous disk swirling around the Sun.  Strong support for the idea comes from the numerous examples of disks that have been spotted elsewhere in the Milky Way. Yet the mathematics that describes such systems reveals a disturbing paradox:  the gravitational pull of a disk can steal orbital energy away from a planet as it’s forming. Instead of maintaining a safe and steady orbit, the equations suggest the young Earth should have been locked in a death spiral that sent it plunging into the Sun.

There is, of course, some compelling evidence to the contrary.  “We’re still here!”  says Mac Low.

Now, together with collaborators Wladimir Lyra and Simje-Jan Paardekooper, Mac Low has apparently found a loophole that allows planets like Earth to survive their origins. Continue reading →

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Early exit or long goobye? (illustration courtesy Barry Roal Carlsen, University of Wisconsin-Madison).

Nothing kills a beautiful theory faster than an ugly fact, to paraphrase Thomas Huxley. But what happens when you have three competing theories and two new facts that point in opposite directions? Welcome to the increasingly confusing picture of what happened to the mammoths and mastodons of North America, along with the other dominant mammal species of the late Pleistocene.

For a number of years, scientists have been debating over two possible culprits that might explain the big die off of megafauna. One is severe climate change, brought about by the onset of the Younger Dryas global cooling event. Another is overhunting by a newly arrived human population in North America known as the Clovis culture. More recently, a third hypothesis claims that a comet impact or airburst over the Laurentide ice sheet triggered the changes that caused the animal population collapse.

All of these scenarios, or any combination of them, hinge on the fact that the big mammals died off rather abruptly starting around 12,900 years ago. This matches the onset of the climate change and comes right after Clovis appears on the scene. It also coincides with evidence that appears to supports the comet hypothesis, including lots of tiny “nanodiamonds”, which proponents say may have been generated in the impact and subsequent fires.

Up till now, the debate has revolved around what happened. Now there are new questions about when it happened.

Continue reading →

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Too strange by half? The neutron star at the heart of Cas A has always been an odd ball. (NASA/CXC/M.Weiss/Southampton/W.Ho)

Call it the story of the young and the quarkless:  Astronomers have a surprising new take on the youngest supernova remnant in our corner of the Milky Way, and it may solve a long standing mystery.

The object in questions is Cas A (rhymes with passé) a glowing wreath of energized gas that was discovered years ago in the constellation Cassiopeia.  Cas A was created when a massive star reached the end of its nuclear rope about three centuries ago and proceeded to blow itself to smithereens.  What’s left at the centre is a tiny nugget of superdense matter called a neutron star, the youngest example of one we know.

So far, so good.  But there’s always been something weird about the neutron star in Cas A since it was first spotted by the Chandra X-ray Observatory in 1999. Now it looks like there’s an explanation.

Continue reading →

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Fermi: sneaking a peak at the dark side. (NASA/GSFC)

A team of Harvard and NYU researchers has upped the ante in the race to discover the true nature of dark matter. 

In a new paper posted online this week, the team says NASA’s Fermi satellite has confirmed the existence of a vast cloud of energetic electrons surrounding the centre of our galaxy—electrons, they suggest, which could be subatomic shrapnel from dark matter particles colliding with one another.

If correct, their interpretation of the Fermi data would tie together a number of hints and puzzling observations that suggest dark matter is making itself visible through a process of annihilation.  It also implies the existence of a new force to which only dark matter particles are attuned.

 “It’s very easy to produce this kind of a signal with dark matter,” says Doug Finkbeiner of the Harvard-Smithsonian Center for Astrophysics, who is a co-author of the paper. “It’s not so easy to do it with other things.” Continue reading →

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A simulated image of the disk of gas surrounding the supermassive black hole at the centre of the Milky Way as it might appear with new methods designed to reveal the black hole's dark edge. The light-bending effects of the black hole's strong gravitational field as well as the disk's rapid rotation would produce a crescent shaped image wrapped around the event horizon. (Credit: Avery Broderick)

A black hole is like a scary monster from children’s literature.  It’s vividly imagined but never actually seen in real life. This is true even for the largest black holes we know—the ones that reside at the centres of galaxies. The nearest of these lies some 30,000 light years away, in the core of the Milky Way. If you placed it in our solar system it would probably span the orbit of Mercury. Yet, because of its great distance, it’s a mere speck against the sky, about 36 million times smaller than the full moon. How could anyone see any detail when looking at something with an apparent size THAT small?

Amazingly, there is a way.  And now it’s promising not only to reveal the giant black hole in our own galaxy, but also a much larger and more active one in the galaxy known as M87 in Virgo.

Continue reading →

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Smoke billows from backfires set to deplete fuel around the Mt. Wilson observatory. (LA Times)

What do you do when a raging wildfire threatens to engulf your observatory? You light backfires, spray fire retardant and water bomb the slopes… but mostly you just hope for good luck.

Last month, the Mt. Wilson Observatory got a welcome dose of good luck when it escaped destruction by the notorious Station Fire, which burned out of control for weeks in the mountainous woodlands north of Los Angeles.

Mt. Wilson is home to the 100-inch Hooker telescope, one of the most storied instruments in the history of astronomy. It’s here that Edwin Hubble gathered the crucial evidence that allowed him to demonstrate, in 1925, that the universe is much, much bigger than previously thought. 

In this episode of The Universe in Mind podcast, Harold McAllister, director of the Mt. Wison Instiute, talks about the observatory’s brush with oblivion.  Marcia Bartusiak, author of The Day We Found the Universe explains how Hubble’s work on Mt. Wilson was the culmination of an amazing epoch of discovery that saw the cutting edge of observational astronomy migrate from Europe to the New World.  

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Throw in a magnetic field and the fate of the "evaporating" planet HD209458b gets foggy. Illustration: European Space Agency, Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS, France) and NASA

Do planets around other stars have magnetic fields? It may seem an esoteric question, but life as we know it—at least terrestrial life—could not survive on Earth without the magnetic umbrella that protects us from an onslaught of hard solar radiation.

Now it appears a planet that is light years from our own may be depending on a magnetic field for its continued existence.

The planet in question is HD209458b. Admittedly, it’s more of a serial number than a name, but to astronomers it’s one of the most infamous handles in the galaxy. 

Continue reading →

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Shuffling into oblivion: Did a comet wipe out the great mammals of North America? (Source: PLoS Biology)

At the end of the last ice age North America was in the midst of an epic thaw. The giant glaciers that had covered nearly all of Canada and the northern United State for millennia were receding fast.  Spring was in the air.

This was, presumably, good news for all the exotic creatures that populated North America at the time, including the mammoths, mastadons, giant sloths, sabre tooth cats, dire wolves and several other large species, collectively known as the Pleistocene megafauna. It was also good news for the Clovis people, a population of Paleolithic hunters that found their way into North America from Siberia, via an ice free corridor that ran just east of the rockies.  They had plenty of big game to live on, as their kill sites demonstrate.

So what happened?

Continue reading →

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Good vibrations. Gravity waves offer a entirely new way to perceive events such as the collisions of black holes. (Illustration: W. Benger, Zuse Institute Berlin/Max-Planck Institute for Gravitational Physics)

Astronomy is the ultimate “seeing” science.  Unlike our experience of everyday reality, there’s no sound out in the cosmos, so the processes and events that we observe in the universe unfold before us like a silent movie.

Now some researchers are trying to add a soundtrack to that movie. They are the ones searching for gravitational waves—ripples in spacetime caused by the rapid motion of massive objects. If detected these waves will offer an entirely new way to perceive the universe—one that has more in common with hearing than seeing.

In Episode #11 of The Universe in Mind podcast we hear from Neil Cornish (Montana State University, Bozeman) about recent progress in the hunt for gravitational waves, and we get a bold prediction for how soon these elusive but revealing signals will be detected.

Jacqueline Radigan of the University of Toronto also drops by to explain how brown dwarfs—objects that are midway between stars and planets—can have their own weather patterns

Enjoy the program!

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