largest black holes discovered by scientists

Scientists have discovered the largest black holes yet, and they're far bigger than researchers expected based on the galaxies in which they were found.

An artist's rendition of a mammoth black hole, NASA

The discovery suggests we have much to learn about how monster black holes grow, scientists said.

All large galaxies are thought to harbor super-massive black holes at their hearts that contain millions to billions of times the mass of our sun. Until now, the largest black hole known was a mammoth dwelling in the giant elliptical galaxy Messier 87. This black hole has a mass 6.3 billion times that of the sun.
Now research suggests black holes in two nearby galaxies are even bigger.

The scientists used the Gemini and Keck observatories in Hawaii and the McDonald Observatory in Texas to monitor the velocities of stars orbiting around the centers of a pair of galaxies. These velocities reveal the strength of the gravitational pull on those stars, which in turn is linked with the masses of the black holes lurking there.

The new findings suggest that one galaxy, known as NGC 3842, the brightest galaxy in the Leo cluster of galaxies nearly 320 million light years distant, has a central black hole 9.7 billion solar masses large. The other, named NGC 4889, the brightest galaxy in the Coma cluster more than 335 million light years away, has a black hole of comparable or larger mass. Both encompass regions or "event horizons" about five times the distance from the sun to Pluto.

Astronomers had suspected that black holes more than 10 billion solar masses large exist, based on light from quasars, cosmic objects from the early universe that are no more than a light year or two across but are thousands of times brighter than our entire galaxy.

The light of quasars is thought to come from matter driven to incandescent brightness as it spirals at high speeds into supermassive black holes. This is the first time scientists have detected black holes approaching such theorized giants in size.

This pair of black holes is 1.6 to 4.6 times more massive than one would predict from their galaxies, based on details such as the brightness of the bulges at their centers. These findings suggest that black holes may grow differently in large galaxies than in small ones.

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Life-Bearing Lake discovered on Icy Jupiter Moon Europa

    A large lake discovered just below Europa's icy shell may provide a habitat for life.

As this Galileo probe image shows, Europa's icy surface is cracked and jumbled -- an indication of a sub-surface heat source. Click to enlarge this image. NASA

New research shows the jumbled ice blocks crowning the surface of Jupiter's icy moon Europa are signs of a large liquid lake the volume of the North American Great Lakes just below the surface, a key finding in the search for places where life might exist beyond Earth.
Drawing from studies of underground volcanoes in Iceland and Antarctica, scientists ran computer models to see if the chaotic formations on Europa's surface could be explained by the same geologic processes seen on Earth.
"We looked at melt underneath the ice and the fracture and collapse of ice shelves," Britney Schmidt, a postdoctoral fellow at the University of Texas at Austin's Institute for Geophysics, told Discovery News.
"We come with these large pockets of water that form lakes. As they melt they actually break up the ice above it, like what you see on Earth," she said.
"This is certainly the best model so far," Paul Schenk, a staff scientist with the Lunar and Planetary Institute in Houston, wrote in an email to Discovery News. "If we go back with penetrating radar instruments we should be able to see into the ice shell, determine the stratigraphy of the layers in the shell and verify which models works best."
Europa, which is slightly smaller than Earth's moon, is believed to have a large ocean of salty water deep beneath its frozen crust. These recently discovered lakes appear to be embedded closer to the surface.
"Europa has more water than all of Earth's oceans," planetary scientist Simon Kattenhorn, with the University of Idaho, exclaimed.
While the ocean itself is of interest to scientists searching for life beyond Earth, a mechanism to churn the surface ice and subsurface water makes Europa an even more compelling target.
The vigorous mixing of ice and water provides one mechanism for nutrients and energy to get from the frozen surface to the ocean below.
"It's exciting for biology," Schmidt said.
A mission to Europa is second on planetary scientists' wish list after a sample return mission from Mars.
"Europa is likely to have a deep ocean of liquid water beneath its icy crust, making it an object of enormous interest as a possible abode for life," planetary scientist Steve Squyres, with Cornell University, testified at a Congressional hearing this week.
Schmidt's research will be published in a future issue of Nature and appears on the publication's website Wednesday.

© Discovery News
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Two Dwarfs Spotted Hanging-Out With Andromeda

Our galaxy lives in a pretty typical, boring region of of the cosmic web of galaxies in what we call "The Local Group." It is dominated by Andromeda and the Milky Way, but has a whole host of smaller galaxies associated with these two giants.

Images: Top - Andromeda XXIX, outlined in yellow for clarity. Credit - Gemini Observatory/AURA/Eric Bell; Middle - Model of the Local Group. Credit - Richard Powell; Bottom - It's not that obvious in the sky, but the Sagittarius dwarf galaxy has left a stream of stars around the Milky Way. Credit - David Law, UCLA.

Most of these galaxies are dwarf galaxies, and this shouldn't be too surprising. From planetary bodies to stars to galaxies, the universe tends to make a lot of "little" things and very few spectacularly large ones.
There are something like a hundred galaxies in the Local Group when you add up all the dwarf galaxies. The exact number is hard to determine, as there is some debate over whether some objects are "really" galaxies or just a chance grouping of stars.
These two new dwarf galaxies are named Andromeda XXVIII and Andromeda XXIX, because, again, astronomers are so clever at naming things, and these are the 28th and 29th dwarf galaxies to be found associated with the Andromeda Galaxy. Both are actually a bit far removed from the large spiral, and thus may clue us in to how dwarf galaxies look before they get too close to a big galaxy.
What happens when a little galaxy gets too close? Well, just ask the famous Sagittarius dwarf galaxy, if you can. It's been gravitationally ripped to shreds, leaving a stream of stars looping around the Milky Way at least twice. The "galactic cannibalism" is how large galaxies grow larger over time, consuming the myriad of smaller galaxies.
Since these galaxies are so faint, we can really only study the ones that live in our Local Group and extrapolate to other galaxy groups. However, being in the middle of our galaxy's disk means that our view isn't necessarily unobstructed.
Finding and classifying new dwarf galaxies is painstaking work. Will there ever be an end? Will there be something too small to classify as a galaxy and a Pluto-like debate over its name? Probably, but finding out how the universe works is way more interesting than agonizing over a name.
This research has been published in Astrophysical Journal Letters, and the preprints can be found at arxiv.org.
Discovery News

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Strange Hollows Discovered on Mercury

Oct 24, 2011: NASA's MESSENGER spacecraft has discovered strange hollows on the surface of Mercury. Images taken from orbit reveal thousands of peculiar depressions at a variety of longitudes and latitudes, ranging in size from 60 feet to over a mile across and 60 to 120 feet deep. No one knows how they got there.
(Image on the left-Hollows inside the Raditladi impact basin. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

"These hollows were a major surprise," says David Blewett, science team member from the Johns Hopkins University Applied Physics Laboratory. "We've been thinking of Mercury as a relic – a place that's really not changing much anymore, except by impact cratering. But the hollows appear to be younger than the craters in which they are found, and that means Mercury's surface is still evolving in a surprising way."
Mars Reconnaissance Orbiter spotted similar depressions in the carbon dioxide ice at Mars' south pole, giving that surface a "swiss cheese" appearance. But on Mercury they're found in rock and often have bright interiors and halos.

"We've never seen anything quite like this on a rocky surface."

If you could stand in one of these "sleepy" hollows on Mercury's surface, you'd find yourself, like Ichabod Crane, in a quiet, still, haunting place, with a black sky above your head.
"There's essentially no atmosphere on Mercury," explains Blewett. "And with no atmosphere, wind doesn't blow and rain doesn't fall. So the hollows weren't carved by wind or water. Other forces must be at work."
As the planet closest to the Sun, Mercury is exposed to fierce heat and extreme space weather. Blewett believes these factors play a role.

 Another example of hollows in crater Tyagaraja. Courtesy Science/AAAS

A key clue, he says, is that many of the hollows are associated with central mounds or mountains inside Mercury's impact craters. These so-called “peak rings” are thought to be made of material forced up from the depths by the impact that formed the crater. Excavated material could be unstable when it finds itself suddenly exposed at Mercury's surface.
"Certain minerals, for example those that contain sulfur and other volatiles, would be easily vaporized by the onslaught of heat, solar wind, and micrometeoroids that Mercury experiences on a daily basis," he says. "Perhaps sulfur is vaporizing, leaving just the other minerals, and therefore weakening the rock and making it spongier. Then the rock would crumble and erode more readily, forming these depressions."

 A fresh impact crater. Hollows are present on a section of the crater wall that has slid partway down toward the floor. Courtesy  Science/AAAS

MESSENGER has indeed proven Mercury unexpectedly rich in sulfur. That in itself is a surprise that's forcing scientists to rethink how Mercury was formed. The prevailing models suggest that either
(1) very early in Solar System history, during the final sweep-up of the large planetesimals that formed the planets, a colossal impact tore off much of Mercury's rocky outer layering; or
(2) a hot phase of the early Sun heated up the surface enough to scorch off the outer layers. In either case, the elements with a low boiling point – volatiles like sulfur and potassium – would have been driven off.
But they're still there.
"The old models just don't fit with the new data, so we'll have to look at other hypotheses."
To figure out how the planets and Solar System came to be, scientists must understand Mercury.
"It's the anchor at one end of the Solar System. Learning how Mercury formed will have major implications for the rest of the planets. And MESSENGER is showing that, up to now, we've been completely wrong about this little world in so many ways!"
What other surprises does Mercury hold? The sleepy hollows of the innermost planet may be just the beginning.
Credit: Science@NASA

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