Remember a couple of years ago when physicists thought the universe might be a hologram? No? Well, anyway, it turns out the universe is (almost certainly) not a hologram.
Astronomy
Close encounters of the rocky kind
A bus-sized asteroid will “just” miss the Earth today around noon CDT. Asteroid 2011 MD, which is estimated to be 9-30 meters in size, will come within about 7,500 miles of the surface of the Earth, pretty close as far as asteroid encounters go, and well within the 22,000 mile radius of geosynchronous satellite orbits. But for comparison, it is well beyond the 220-mile orbit of the International Space Station. Even at its closest approach, the asteroid will not be visible to the naked eye, but may appear as a bright dot to sharp-eyed observers with medium-sized telescopes.
NASA scientists, who have been tracking asteroid 2011 MD since June 22, say there is “no chance” it will strike the Earth. Even if it did, its rocky composition means it would very likely break apart and burn up in the atmosphere (over Antarctica). The ones you have to watch out for are the rocks made up of iron, which are more likely to survive the trip through the atmosphere.
This isn’t the first close-encounter we’ve had this year. Asteroid 2011 CQ1 came within 3,400 miles of Earth in February, and set a new record as the closest recorded pass ever. NASA estimates that moderate-sized asteroids make close flybys about six times a year, and they have not been able to track all of them — asteroid 2011 CQ1 wasn’t discovered until hours before its closest approach. But the truth is, the Earth is struck by stuff from outer space all the time, and we haven’t experienced a catastrophic event for a very long time. Approximately 500 small meteors make it all the way to the surface of the Earth each year, and it is estimated that about one small asteroid (1-10 meters in size) reaches the Earth per year. The latter usually break up and vaporize in the upper atmosphere. Fortunately, there is an inverse relationship between the size of an object and the frequency with which it is likely to strike the Earth. In other words, the bigger they are, the less likely we are to be hit by one. Here is a comparison of asteroid radius and strike frequency:
- 10 m: every year
- 50 m: every 1,000 years
- 1 km: every 500,000 years
- 5 km: every 10 million years
- 10 km: every 100 million – 1 billion years
The last known very large impact event involving an asteroid about 10 km in size is the one that is believed to have wiped out the dinosaurs 65 million years ago. We’re not due for even a 1 km event until the year 2880 when asteroid (29075) 1950 DA has a possibility of hitting the Earth. So it’s probably okay to carry on with civilization for a while longer.
Sunspot hiatus may mean colder weather ahead
A colorized photo of a sunspot with the Earth shown for scale.
New results from three different studies indicate the Sun is likely entering a prolonged period of low activity, which will have a profound effect on the Earth. Solar scientists base their conclusion on weakening magnetic fields along the poles of the Sun and decreasing intensity of sunspots.
“The solar cycle may be going into a hiatus,” Frank Hill, associate director of the National Solar Observatory’s Solar Synoptic Network, said in a news briefing [June 14].
The studies looked at a missing jet stream in the solar interior, fading sunspots on the sun’s visible surface, and changes in the corona and near the poles.
“This is highly unusual and unexpected,” Hill said. “But the fact that three completely different views of the sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation.”
Since the 1800s, scientists have known that the Sun goes through a cycle in which the number of sunspots visible on the Sun’s surface gradually rises to a maximum and then falls to a minimum, repeating approximately every 11 years. Sunspots are dark patches on the surface of the Sun about the size of the Earth. They appear dark in photos of the Sun, because the plasma in sunspots is relatively cool (~4,500 K) compared with the plasma elsewhere on the surface of the Sun (~5,800 K). The key word is relatively — if you were so unwise as to point your telescope directly at a sunspot, you would still be blinded.
Sunspots usually appear on the surface in pairs, and that is because they are connected by magnetic field lines, which are created and altered by the roiling sea of plasma on the surface of the Sun. Magnetic field lines are kind of like rubber bands in that they can be twisted and stretched, and sometimes this twisting action causes magnetic field lines to get wound up and extend out from the surface of the Sun. Sunspot pairs are observed where the lines poke out from the surface (see below). The reason the temperature of sunspots is lower than the surrounding region is that the magnetic field lines prevent hotter plasma from flowing into those areas.
During the solar maximum, when the number of visible sunspots reaches a peak, the Sun’s magnetic field actually flip-flops. If you think of the Sun as sort of like a gigantic bar magnet, this means the south magnetic pole becomes the north magnetic pole, and vice versa. The Sun thus has a solar cycle that lasts about 22 years, since this is how long it takes for the Sun’s magnetic field to return to its previous polarity.
Solar scientists believe that the current maximum may be the last we’ll see for decades, and this has profound implications for the Earth’s climate. The sunspot cycle repeats fairly regularly, but the intensity of the sunspot cycle can change dramatically. In the late 1950s there was a particularly strong solar maximum, and in the period 1645 to 1715 there was virtually no sunspot activity at all. The latter period is referred to as the Maunder minimum (after the astronomer who discovered it in observational records1). The significance of the Maunder minimum is that it coincided with a prolonged period of exceptionally cold weather in Europe and North America, referred to as the Little Ice Age. This is part of a general trend of colder periods coinciding with solar minima. If we are entering another prolonged period devoid of solar maxima, it is likely we will experience a prolonged period of cooler weather.
Active black hole twins discovered in center of galaxy
In a surprise discovery, astronomers using the Burst Alert Telescope aboard the Swift satellite learned that both supermassive black holes in galaxy Mrk 7391 (yes, it has two) are actively feeding on material. (Check out the link for a cool vid of the galaxy.) Mrk 739 is a mere 425 million light-years from Earth, making it the second-closest active pair of supermassive black holes to Earth. (The first-closest is in galaxy NGC 6240.)
So, besides the sheer coolness of two supermassive black holes in a single galaxy, why do astronomers care about such objects? As it turns out, they are an important key to understanding galaxy evolution.
Nearly every galaxy, including our own Milky Way, harbors a supermassive black hole in its nucleus, but only a few percent of those black holes are observed to be actively feeding on significant amounts of gaseous and stellar material. Such systems are referred to as active galactic nuclei or AGN for short, and they are believed to be a temporary stage through which all galaxies harboring supermassive black holes pass. During this relatively brief active period, typically lasting ~50 million years, the gaseous material AGN feed on becomes superheated as it spirals down onto the black hole, causing AGN to shine very brightly. The intense brightness means these objects are often observable at very great distances, and therefore over a big range of cosmic history. This is why AGN are important probes of galaxy evolution.
Astronomers aren’t entirely sure what drives this material from the outskirts of the galaxy all the way down to the black hole, but it has been posited that galaxy interactions, including major mergers like the one shown below, are a likely mechanism.
What’s happening here is that the mutual gravitational tugging on gas orbiting in the galactic disks causes it to lose angular momentum and travel inward toward the nucleus of at least one galaxy, and possibly both, eventually reaching one or both of the black holes. If both black holes are active, the object is referred to as a binary AGN. As the hypothesis goes, such objects should be abundant but short-lived (in cosmic terms), lasting a few to tens of millions of years depending on the distance between the black holes. Eventually, the black holes spiral down to merge into a single, more massive black hole, and the two galaxies become a single, more massive galaxy.
It is a fact that galaxies frequently merge — there are several striking examples of this — but whether they are a major mechanism for creating AGN is another matter. I am a co-author on several papers involving searches for binary black holes, including binary AGN and recoiling black hole pairs, and I have been somewhat surprised by the relatively low frequency with which we observe genuine binary AGN — about 100 times less than the predicted frequency. This implies: 1) the measurements needed to make such detections at large distances are so fine that we are not detecting the vast majority of such objects; or 2) perhaps the notion that mergers play a major role in creating AGN needs to be reconsidered.
Possible dark matter detection
Dark matter detector prototype similar to the ones used in the recent experiment
University of Chicago physicists have discovered signals that are consistent with WIMPs — weakly-interacting massive particles — the leading candidates for dark matter. The signals were measured in a laboratory apparatus that is buried deep below the surface of the Earth in an abandoned mine in Minnesota, where layers of rock prevent cosmic rays and radiation from interfering with the experiment. Oddly enough, physicists discovered that the signal counts were higher in the summer than in the winter, but it sort of makes sense: in the summer months the Earth’s rotation is aligned with the motion of the Sun through the disk of the Milky Way, creating a net velocity through the dark matter cloud that is theorized to envelope our galaxy.
These results are not confirmation of the existence of dark matter, but they are encouraging nonetheless, especially as they are consistent with results from ten years ago that were deemed controversial at the time.
New class of supernova intrigues astronomers
The Palomar Transient Factory (PTF) at Caltech has discovered a new class of bright supernovae that has astronomers baffled. The properties of these objects — extreme brightness, high ultraviolet luminosity, the presence of oxygen and lack of metals common to most supernovae — are not explained by current theoretical models. PTF astronomers speculate that these objects could be the result of exploding supermassive stars with 100 times the mass of the Sun or perhaps even magnetars (rapidly rotating neutron stars with super-strong magnetic fields).
The PTF uses an automated system that includes a telescope that scans large portions of the sky night after night using a wide-field imaging camera, and an algorithm that looks for transients — anything that has varied in brightness and/or position — by comparing these images with images from previous nights. When a transient is discovered, its coordinates are automatically sent to a larger telescope at Palomar for further observation. Finally, if the transient turns out to be interesting enough, an actual astronomer will follow-up with even more observations on an even bigger telescope.
This turns out to be an excellent way to pore over the sky looking for supernovae, which are exceedingly short-lived as cosmic events go — a typical supernova will begin to fade after just a few weeks. Prior to automated sky searches like PTF, this meant that catching a supernova in the act was to a large degree a matter of luck. Even though they’re extremely luminous events, most supernovae occur in galaxies that are so far away that they appear as faint dots in astronomical images. Yet there’s a universe potentially brimming over with them. Astronomers estimate that one in every 100 Milky Way-like galaxies will experience a supernova event each year. With about a hundred billion galaxies in the observable universe — about 20% of which are spirals like the Milky Way — that’s potentially hundreds of millions of events every year, and obviously astronomers want to catch as many of them as they can.
Stunning southern vistas with the VLT Survey Telescope
Wired Science has posted a photo gallery of the new VLT Survey Telescope (VST) in Chile, including VST’s first breathtaking photos of the Southern sky.
The VST is a celestial scout of sorts — its purpose is to take vivid photos of celestial objects and identify suitable candidates for more detailed study by the VLT (Very Large Telescope). The VLT is an array of four large telescopes — each 8.2-m in diameter — with a combined resolution of 1 milli-arcsecond. In practical terms, this means the VLT would be able to distinguish two astronauts standing five feet apart on the surface of the Moon. Since time on the VLT is very precious, the VST — with its impressive 268-megapixel wide-field imaging camera — will be invaluable in selecting optimum targets for it.
Earth-Moon system perhaps not all that rare
Until recently, our Earth-Moon system was thought to be a rare configuration — most moons in the Solar System are proportionally very small compared to the planets they orbit, but our Moon is proportionally large at about one-quarter the size of Earth. Now, results from a new computer simulation conducted by physicists in Zurich and Colorado indicate that such a configuration may be more common than previously thought.
Our Moon is believed to have formed 100 million years after the initial formation of the Solar System when a Mars-sized planet collided with Earth, breaking the smaller planet apart, and forming a debris ring that eventually coalesced into what is now the Moon. According to the simulations, there is about a one in 12 chance of a similar scenario occurring in other systems.
While interesting, keep in mind that these are simulations, not observations, and they do not take into account all of the different variables. They simply tell us that formation of other planets with proportionally large moons is plausible.
Saturday science smorgasbord
Danish inventors successfully launch homemade rocket.
Using money from private donations, space enthusiasts and at least one former NASA employee constructed and successfully launched their own rocket from a floating platform in the sea. The prototype cost $73,000 — extremely cheap as far as rockets go, and no wonder: the components included a hair dryer that was intended to keep a valve from freezing. The rocket was dubbed ‘Heat-1X Tycho Brahe’ after the famous 16th century Danish astronomer.
‘Gang of four’ awarded a $500,000 cosmology prize for their work in dark matter.
Dark matter was first posited to exist in 1934 by astronomer Fritz Zwicky to explain the strange behavior of visible matter spinning around in galaxies. Since that time, detailed observations and complex computer simulations, like those of the prize-winning cosmologists, have helped pin down exactly how much dark matter is in the universe and how it’s distributed.
Thirty years ago, nobody really knew how matter was distributed in the universe on a large scale. Today we know from observations that matter is distributed in cosmic clumps, chains, and filaments surrounding enormous voids. Results from computer models reproduced these features using slow-moving massive dark matter particles, giving cosmologists confidence that dark matter was indeed a major constituent of the universe.
Infrared mapping “masterpiece” shows the universe in 3D.
The map shows two dimensions in terms of celestial longitude and latitude, with a third dimension added by redshift, an indicator of cosmic distance. The map is a culmination of decades of survey work that includes 45,000 galaxies in the local universe.
Milky Way twin
If you ever wondered what the Milky Way (probably) looks like from the outside, check this out.
Our twin is galaxy NGC 6744, residing about 30 million light-years from the Milky Way in the southern constellation of Pavo. That’s pretty close as cosmic distances go. It’s also quite a large galaxy — about 200,000 light-years across, which is twice the size of the Milky Way. If you could see it with your naked eye, it would appear about two-thirds the apparent size of the full moon.
SixDay Science 