Black Hole's Mystery 'Wave' Surprises Scientists

This image is a simulation of the X-ray binary system Swift J1357.2-0933, a black hole and star system, in which the effect of a strange, vertical mystery structure are at their maximum.

CREDIT: Gabriel Perez Diaz, Instituto de Astrofisica de Canarias (Servicio MultiMedia)

Astronomers studying an unusual black hole system have spotted a never-before-seen structure in the disk of matter encircling the system.

Swift J1357.2, an X-ray binary system that regularly emits outbursts of high energy, consists of a black hole slowly consuming its companion star. Matter from the doomed star falls into the accretion disk, which surrounds the black hole, feeding it dust and gas.

While observing the system, a team of scientists noticed an unusual vertical feature traveling through the material.

"It's the first time we can resolve such [a] structure in an accretion disk, and it might be ubiquitous in X-ray binaries during the outburst state," Jesus Corral-Santana, of the Astrophysical Institute of the Canary Islands in Spain, reported.

A hidden structure
The black hole contained in Swift J1357.2 is one of the millions of stellar black holes that dot the Milky Way galaxy.

About three times as massive as the sun, the behemoth likely formed when a single star collapsed inward on itself. The resulting, city-sized body packed a great deal of mass into a tiny package, creating a strong gravitational pull on nearby dust and gas.

Located in the Virgo constellation, approximately 4,900 light-years from Earth, Swift J1357.2 also contains a small companion star, which has only a quarter the mass of the sun.

This companion star orbits the pair's center of mass every 2.8 hours, one of the shortest known orbital periods for such systems.

The black hole pulls material from the companion star into its accretion disk, occasionally emitting the X-ray bursts that enabled scientists to find this otherwise hard-to-spot system, researchers said.

Corral-Santana and his team took hundreds of optical images of the system using the Isaac Newton and the William Herschel Telescopes, both of which are in the Canary Islands.

Studying the light produced by the accretion disk, the researchers noticed a periodic dimming in the system, sometimes occurring over the course of only a few seconds.

"Since the orbital period of the system is 2.8 hours, those dips cannot be produced by eclipses of the companion star. They are much faster," Corral-Santana said.

"Therefore, they must be produced by a hidden structure placed very close to the black hole, in the inner accretion disk."

The new find can only been seen in the outer, optical portion of the accretion disk, not on the inside, where X-ray bursts originate.

The X-ray emission, which shows no periodic variation, unlike its optical counterpart, indicated a vertical structure was hiding the black hole, Corral-Santana said.

Rather than appearing at a set, predictable time, the structure shows up over a steadily increasing period, indicating a wave-like movement through the accretion disk.

"It is a wave produced in the accretion disk, moving outward," Corral-Santana said, "like the wave produced when a stone is dropped in calm water."

The wave-like feature also provides information about the orientation of the black hole.

Objects in space face Earth at a variety of angles, or inclinations. They can be seen edge-on, face-on or somewhere in between. Swift J1357.2 is the only one of 50 suspected similar black-hole systems found with an edge-on accretion disk — what scientists call a high inclination.

However, astronomers think approximately 20 percent of these systems should provide such a perspective.

In order to see the wave-like structure in the accretion disk, scientists must have such an edge-on view of the disk, or one close to it.

A view from a lower inclination, closer to face-on, would not reveal the sudden rises and falls in the total light coming from the system.

"Swift J1357.2 is the prototype of the hitherto missing population of high-inclination black holes in transient X-ray binaries," Corral-Santana said.

Because Swift J1357.2 is the first such system to allow such an edge-on view, the presence of the vertical structure takes on an added significance.

No signs of such structures appear in other similar systems, but that could result simply from their unfortunate angles.

Such structures could in fact exist in other, previously discovered transient X-ray binary systems, hidden only by their observational angles.

The findings were published online today (Feb 28) in the journal Science.

NASA Mars Rover Curiosity Image: Rock named 'Jake Matijevic' Holds Surprises

This image shows where NASA's Curiosity rover aimed two different instruments to study a rock known as "Jake Matijevic" in late September 2012. 

The red dots indicate where Curiosity fired its laser at the rock. 

The circular black and white images are ChemCam images to examine the laser burns. 

Purple circles show spots where Curiosity used its Alpha Particle X-ray Spectrometer (APXS) to study the rock.

CREDIT: NASA/JPL-Caltech/MSSS

NASA Mercury Messenger Finds Surprises

On its third swing past Mercury, NASA’s Mercury Messenger spacecraft discovered an unexpectedly young lava plain, rapid rufflings of the planet’s weak magnetic field and an unanticipated dance of elements in the thin atmosphere.

“I think the biggest surprise for the community is that the planet is turning out to be much more dynamic than people appreciated,” said Sean C. Solomon of the Carnegie Institution of Washington who is the principal investigator for the Messenger mission.

The flyby occurred in September, when the spacecraft swooped within 142 miles of Mercury’s surface at 12,000 miles per hour, but the findings of that flyby just appeared in three papers the journal Science published last week on its Web site.

Within the 180-mile-wide double-ring Rachmaninoff crater, Messenger photographed flat, smooth plains that scientists interpreted as the hardened outflow of lava. Based on the number of smaller impact craters, the age of the volcanic deposits within Rachmaninoff is probably less than two billion years, said Louise K. Procktor of the Johns Hopkins University Applied Physics Laboratory and lead author of the paper that examined the crater.

While not recent, that would still suggest that Mercury was volcanically active well into its middle age, given that it formed 4.5 billion years ago with the rest of the solar system.

“It is quite a big surprise,” Dr. Procktor said.

Mercury, not much more than 3,000 miles in diameter, is by far the smallest of the planets, and thus many thought it would have cooled off in less than a billion years. But Mercury’s mantle may not rise and fall in convective patterns as in larger planets like Earth, and that may have kept the heat inside for more than two billion years. By imparting heat and relieving pressure, the impact of the meteoroid that formed the crater may have helped melt rocks that were already close to melting point.

Messenger’s measurements also detected rapid fluctuations in Mercury’s magnetic field as it shifted from one side of the planet to the other. Such fluctuations occur around Earth in a matter of hours. Around Mercury, the fields shifted in minutes.

“It looked as though we were seeing a complete collapse of the magnetic field,” Dr. Solomon said. “This is an incredibly dynamic magnetosphere.”

The third paper looked at Mercury’s tenuous atmosphere, which consists of atoms knocked off the surface by sunlight, charged particles and dust-size meteoroids. One surprise was that near the equator, the concentration of calcium was higher near sunrise than sunset, but that effect was not seen for sodium or magnesium.

Because only calcium and not the other elements exhibits this behavior, “We can’t explain it,” said Ronald J. Vervack Jr., another scientist at the Johns Hopkins laboratory and lead author of that Science paper. “They just don’t look the same, and they don’t look the same anywhere we look,” he said. “Which is a bit puzzling, because we expected there to be some similarities.”

A tail of sodium that had been seen behind Mercury during the first two flybys, in January 2008 and October 2008, was much diminished in the third flyby. The reason was that Mercury was in a different part of its elliptical orbit, and the resulting change in velocity diminished the power of sunlight that was sweeping the sodium atoms away from Mercury into the tail.

A clearer picture should start to emerge next year. The spacecraft, launched in 2004, has been doing a gravitational do-si-do with the inner planets to slow down as it spirals inward and gets in position to enter orbit around Mercury in March.