Milky Way’s black hole pulling in gas cloud
The destruction is only beginning
By Andrew Grant
An ill-fated gas cloud has begun a close encounter with the monstrous black hole at the center of the Milky Way, a fresh set of observations reveals. Astronomers don’t expect the cloud to emerge intact, resulting in an unprecedented view of our galaxy’s largest black hole feasting on its prey.
In December 2011, astronomers identified the gas cloud, called G2, and found that its orbit would bring it perilously close to the Milky Way’s central black hole by mid-2013. Nineteen months ago, the immense gravity of the black hole, which weighs in at about 4.3 million times the mass of the sun, was already squeezing and stretching the gas cloud as if it were pasta dough.
Now images captured in April with the Very Large Telescope in Chile show that the leading edge of G2 has whipped around the black hole’s far side. “The line of sight is such that the gas cloud is falling away from us toward the black hole,” says Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. “Some material swung by the back side of the black hole and is now flying toward us.”
“If you think of the cloud as a roller coaster train, the first carriage has already swung by the black hole,” Gillessen says. “The main part of the train is still in approach.”
The gas cloud is whizzing through space at up to 3,000 kilometers per second, 100 times the speed at which Earth orbits the sun and a whopping 1 percent of the speed of light. In just a few months, the black hole has not only accelerated the cloud to those speeds, but reversed the motion of the front side a full 180 degrees. The findings will appear in an upcomingAstrophysical Journal.
Gillessen and his team also found that the black hole has stretched G2 to twice its length last year. As a result, the researchers predict that the bulk of the cloud won’t make its closest approach to the black hole until early next year. When that happens, telescopes around the world will point at the galactic center to capture the drama.
Dimitrios Giannios, an astrophysicist at Purdue University in West Lafayette, Ind., does not expect G2 to survive its encounter with the galaxy’s central black hole. The cloud will probably fade from view in coming months as it continues to stretch out, he says. But its remnants might gradually get funneled into the black hole within a few decades, culminating in a rare bright display as they approach the point of no return. “It would be a last echo of the death of this cloud,” he says.
Size isn’t only mystery of huge virus
Strange replication method and unusual genetic sequence among the mysteries
The largest virus ever identified has been found on the seafloor off the coast of Chile.Pandoravirus salinus is about twice as long as the previous record holder, Megavirus chilensis, with a genome that is twice as large. That makes P. salinus larger than the smallest bacteria.
Beyond its impressive size, the Pandoravirus is strange in some other ways. Rather than reproducing by first making a viral coat and then filling it in or by building its coat around genetic material, P. salinus builds its insides and outsides simultaneously, starting at one end of the horseshoe-shaped viral particle and finishing at the other. What’s more, only 7 percent of the virus’s genes match any known gene sequences, researchers report in the July 19 Science.
The authors suggest a controversial hypothesis for why the Pandoravirus is so odd: It could have evolved from a type of free-living, ancient cell that no longer exists. Its discovery is likely to add fuel to the heated debate about the evolutionary origins of viruses.
Stem cells made with just seven chemicals
Cocktail of molecules turns adult mouse cells into embryonic-like ones
By Meghan Rosen
Whipping up a batch of stem cells just got easier.
A new recipe for transforming adult cells into embryonic-like ones calls for a chemical cocktail to erase signs of age. By adding just seven small molecules, scientists can turn back time for mature mouse cells, converting them into pluripotent stem cells. These cells hover at the brink of developing into virtually any type of tissue.
Researchers have previously created pluripotent stem cells using cloning, or by dosing a dish of adult cells with “master genes” that flip grown-up cells back to a youthful state. But cloning cells and tinkering with genes can be expensive and technically tricky.
So biologist Pingping Hou of Peking University in Beijing and colleagues scoured a collection of about 10,000 chemicals and found a combination that mimicked the cell-programming effects of master genes. Adding the combo to adult mouse cells turned them into pluripotent stem cells, which the researchers could then make into brain, lung or muscle tissue, Hou and colleagues report July 18 in Science.
If the chemical method works in human cells, it could one day make stem cells for medical use, the researchers suggest.
Mars meteorite reveals its age
Long difficult to estimate, date of space rocks’ formation emerges with new technique
By Andrew Grant
Providing a tool for unlocking secrets of the early solar system, a new technique accurately determines the age of meteorites, scientists report in the July 25 Nature.
Scientists disagree over estimates of meteorites’ ages because it’s hard to distinguish between when the rocks formed and when they got seared from an impact and flung into space toward Earth.
UCLA geochronologist Axel Schmitt and colleagues began by examining the structure of a meteorite’s mineral crystals, which differs depending on whether the crystals solidified gradually within a lava flow or rapidly after the intense heat and pressure of an impact. Then they determined the age of the crystals by measuring the ratio of uranium to lead. Uranium has two isotopes, each of which decays into its own lead isotope, providing researchers with multiple radioactive-dating measurements to cross-check for consistency.
The team analyzed the Martian meteorite Northwest Africa 5298 and found large, interlocking crystals about 187 million years old, which suggests that the rock formed during a volcanic eruption back then. The researchers also found zircon crystals that likely formed from an impact no more than 22 million years ago.
Schmitt says that by applying the technique to rocks from Mars, the moon, asteroids and even Earth, scientists can learn about when volcanoes erupted in the distant past.