Tag Archives: space

Black Hole’s Newly Seen Y-Rays Suggest Recent Activity [Nature]

The quiescent monster at the center of the Milky Way—a supermassive black hole weighing about four million sun—used to be a lot more active.

Ghostly jets seen streaming from Milky Way’s core

Astronomers have found the best evidence yet that the dormant gravitational monster that lies at the centre of the Milky Way — a supermassive black hole known as Sagittarius A* — recently emitted a pair of γ-ray jets.

As they feed on stars and clouds of gas that stray too close, black holes at the centres of other galaxies create bright jets that can be seen across cosmic distances. But the Milky Way’s black hole shows no signs of such activity. Now, the Fermi Gamma-ray Space Telescope has picked up some faint γ-ray signals that suggest that Sagittarius A* has not always been so tranquil. The black hole could even have been active as recently as 20,000 years ago, after gulping down a gas cloud with a mass about 100 times that of the Sun, says Douglas Finkbeiner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Not part of my Nature article, but interesting nonetheless, is that the jets—composed of gamma-ray emitting charged particles—could have inflated the bubbles. To do so, the “faint, pathetic jets” observed by Fermi would have had to be much brighter, and carried more energy, in the past, says Finkbeiner. “We infer that that most of the time over the last million years, the jets have been perhaps ten times as bright.”

He adds that Fermi does not see the jets within about 10,000 light-years of the galaxy’s center, an indication that Sagittarius A* switched off its activity some 20,000 to 30,000 years ago, assuming the jets travel at about one–third the speed of light.

The artist’s illustration below, which shows the jets going all the way to the Milky Way’s center, reflects how the jets used to appear, not how they appear now.

Credit: David A. Aguilar (CfA)
Credit: David A. Aguilar (CfA)

NASA’s Visit to Solar System’s 2nd Biggest Asteroid Vesta Yields New Data about Asteroid Families [Nature]

Vesta confirmed as venerable planet progenitor

NASA’s Dawn spacecraft won’t end its 13-month-long visit to Vesta, the Solar System’s second biggest asteroid, until August, but researchers have now solidified the rock’s reputation as an archetype for understanding planetary evolution. In six reports in the 11 May edition of  Science, Dawn mission scientists have confirmed several long-held assumptions about Vesta and detailed some puzzles about the roughly 520-kilometer-diameter body.

My article highlights Vesta’s importance in our understanding of asteroids and meteorites, as well some remaining mysteries that continued study may illuminate.

Update: The Knight Science Journalism Tracker once again notes my science reporting by highlighting this and my previous Vesta-related story:

NatureNews (blog) Ron Cowen: Vesta confirmed as venerable planet progenitor ; the ‘confirmed’ in the hed is a good way to say this is not surprise news, but incremental news. Cowen, on constant prowl for news before it is wide news, includes a link to a previous post on Vesta’s topography and what it might mean, from meetings last fall.


Where’s the Dark Matter? New Study Finds None Near the Solar System [Nature]

Survey finds no hint of dark matter near Solar System

In the largest survey of its kind to date, astronomers scouring the space around the Solar System for signs of dark matter — the hypothetical material believed to account for more than 80% of the mass in the Universe — have come up empty-handed.

If confirmed, the surprising result would upend a long-established consensus, researchers not involved in the study say.  For decades, cosmic theories have relied on dark matter — which exerts gravitational pull but emits no light — to be the hidden scaffolding that explains how structure arose in the Universe, how galaxies formed and how the rapidly spinning Milky Way manages to keep from flying apart. Without dark matter, theorists say, the visible material in the Universe, such as stars and gas, would not have the heft to do the job alone.

The rest of the article explains how the research was conducted and what the scientific community thinks of the finding.

Credit: ESO/H.H.Heyer
Credit: ESO/H.H.Heyer

Exoplanets and the 2012 American Astronomical Society Winter Meeting [NPR Science Friday]

NPR’s Science Friday invited me to talk about exoplanets and the 2012 Winter meeting of the American Astronomical Society:

Kepler Telescope Spots Tiniest Exoplanets Yet

At a meeting of the American Astronomical Society, scientists talked about mapping dark matter, measuring the ‘graininess’ of spacetime, and discovering the smallest exoplanets ever, using the Kepler space telescope. Ron Cowen, who reported on the meeting for Nature, discusses those findings.

Go ahead and listen to me with Ira Flatow on the Science Friday Web site!