• binary black holes
  • Ceres
  • New Horizon's pathway

Ceres Mysteries… Still Mystify

Since settling into orbit around the dwarf planet Ceres in March, NASA’s Dawn spacecraft has slowly been spiraling closer, imaging the little world’s surface at increasing levels of resolution. Currently, it is in its next-to-closest orbit, the “High Altitude Mapping Orbit” (HAMO), 915 miles (1470 kilometers) above the surface, circling once every 19 hours.

Among the curiosities Dawn has imaged are the as-yet-unexplained white spots in Occator Crater and numerous other areas—most likely reflections of sunlight off natural specular surfaces which may be either ice or bright deposits of salt. At certain times, what appears to be a haze has also reported within 60-mile wide Occator and remains as mystifying as are the spots. This observation is apparently being questioned, as some investigators feel that the “haze” may be a photographic artifact. According to principal investigator Christopher Russell, images of the haze and other observations from HAMO have been embargoed until a paper about them is accepted for publication in the scientific journal Nature. Nevertheless, he has described the white spots as looking like a “thick dusting of white powder,” which would tend to discount the ice theory.

Another puzzle that closer views should help to clarify is the nature of a strangely-isolated mountain looming three miles (five kilometers) over an otherwise flat area that was first seen from Dawn’s Survey Orbit, 2,700 miles (4,400 km) high. Apparently the loneliest mountain—and the only one of its kind—on Ceres, this feature is sometimes described as “pyramid-shaped,” although it’s actually somewhat flattened at the top, and its steeply-sloping sides are vertically-streaked with white material of unknown origin.

Dawn’s task at each of its four progressively closer orbital stages is to map the entire surface several times, each time looking at a slightly different angle so that image analysts can figure out the topographical contours such as the depths of craters, the heights of mountains, and the nature of other enigmas on this little world.

–Bing Quock

New Target for New Horizons

In a NASA press release last week, the New Horizons team announced they have settled on the spacecraft’s next recommended target—the eloquently named 2014 MU69, a 30-mile (45-kilometer) wide, icy Kuiper Belt Object (KBO) about one billion miles from the dwarf planet.

Why this target? “2014 MU69 is a great choice because it is just the kind of ancient KBO, formed where it orbits now, that the Decadal Survey desired us to fly by,” said Alan Stern, New Horizons principal investigator. “Moreover, this KBO costs less fuel to reach [than other candidate targets], leaving more fuel for the flyby, for ancillary science, and greater fuel reserves to protect against the unforeseen.”

Identifying a potential target early is critical because a series of four maneuvers in October and November will be needed to get on course and delays in deciding where to go would cost fuel, and potentially the extended mission all together.

Still, the fly by of 2014 MU69 is not a guarantee. The official proposal is due in 2016, after New Horizons’s primary mission data collecting and imaging Pluto and its moon, Charon, is complete. An independent team of experts then needs to evaluate the proposal before NASA can give the go-ahead. If everything is approved and goes according to plan, the far-traveling explorer will reach this new target on January 1, 2019.

Until then, New Horizons is still collecting and sending incredible data and images of the Pluto system, so stay tuned for updates! –Elise Ricard

Citizen Scientists Weigh Stars

What did scientists do before citizen science? Citizen scientists have transformed projects that require big data. Large groups of citizen scientists can classify, identify, and catalog in a short time what it would take one scientist (or a dozen) a lifetime. Take a recent publication about star mass and formation. To examine this topic more closely, astronomers wanted to compare star clusters in the Andromeda galaxy to our own Milky Way galaxy.

That task required poring over 414 mosaic photos of Andromeda taken by the Hubble Space Telescope. “Given the sheer volume of Hubble images, our study… would not have been possible without the help of citizen scientists,” says Daniel Weisz of the University of Washington, and lead author of the new publication.

Stars are born when a giant cloud of molecular hydrogen, dust, and other trace elements collapses. The cloud breaks into small clusters of material that each precipitate hundreds of stars. These stars’ masses can range from 1/12th to a couple hundred times the mass of our sun. By nailing down what percentage of stars have a particular mass within a cluster, what astronomers call the Initial Mass Function (IMF), scientists can better interpret the light from distant galaxies and understand the formation history of stars in our universe.

Over the course of 25 days, 30,000 citizen scientists submitted 1.82 million individual image classifications of star clusters throughout the neighboring galaxy—based on how concentrated the stars were, their shapes, and how well the stars stood out from the background—to the Andromeda Project on Zooniverse.

To the astronomers’ surprise, the IMF was very similar among all the clusters surveyed. But curiously, the brightest and most massive stars in these clusters are 25 percent less abundant than predicted by previous research. Astronomers use the light from these brightest stars to weigh distant star clusters and galaxies and to measure how rapidly the clusters are forming stars. This result suggests that mass estimates using previous work were too low because they assumed that there were too few faint, low-mass stars forming along with the bright, massive stars.

This evidence also implies that the early Universe did not have as many heavy elements for making planets, because there would be fewer supernovae from massive stars to manufacture heavy elements for planet building.

“The efforts of these citizen scientists open the door to a variety of new and interesting scientific investigations, including this new measurement of the IMF,” Weisz says. –Molly Michelson

When One Black Hole Isn’t Enough

A mere 581 million light years distant, Markarian 231 (Mrk 231 to its friends) is the nearest galaxy to host a quasar. Quasars are basically the brightest objects in the Universe, and they reside so far away that they appear as points of light… Which is why, when astronomers discovered the first quasars, they dubbed them “quas(i-stell)ar objects” (QSOs) and then inventively shortened the name.

It turns out that quasars are actually the crazy bright cores of active galaxies. So much energy is created in the centers of these galaxies that they shine amazingly brightly. Astronomers have long suspected that the gravitational energy of supermassive black holes fuels these brilliant beacons, forming accretion disks around the black holes and powering energetic beams in which particles stream away from the black holes at near the speed of light. But because these galaxies reside so far away from us, we can’t see exactly what transpires in their compact cores.

Unless, of course, we use the Hubble Space Telescope to take a gander at the closest quasar!

Astronomers sifted through the Hubble archive, searching for observations of Mrk 231 in ultraviolet light. Why? Because the quasar emits enough energy to heat its surrounding accretion disk and cause it to glow in high-energy, short-wavelength ultraviolet light. Indeed, astronomers found evidence of a hot accretion disk, but with a surprising gap in its middle.

This observation provides evidence for a giant donut hole in the center of the disk! That wouldn’t happen with just one black hole, but two black holes…? As they circle one another, they carve out a region in the center of the disk and create the gap in ultraviolet radiation that astronomers observe.

“We are extremely excited about this finding because it not only shows the existence of a close binary black hole in Mrk 231, but also paves a new way to systematically search binary black holes via the nature of their ultraviolet light emission,” said Youjun Lu of the National Astronomical Observatories of China, Chinese Academy of Sciences.

It turns out that binary black holes might occur relatively frequently in the Universe. We know that galaxies collide with one another all the time, and since basically any good-sized galaxy has a supermassive black hole at its center, two colliding galaxies would give you two supermassive black holes! (We see this in the galaxy NGC 6240, for example.) Eventually, two black holes could end up as a close binary, which is what seems to be happening in Mrk 231… And perhaps end up merging together. –Ryan Wyatt

Image: Binary Black Holes, ASA, ESA, and G. Bacon (STScI); Ceres, NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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