WASHINGTON — An article in last Thursday's Sun on discovery of a super-massive black hole in the galaxy M87 included an incorrect comparison. The speed measurements of gases in M87 were taken at a distance of 60 light years from the galaxy's center. That is equivalent to 15 times the distance from Earth to the nearest star, Alpha Centauri.
The Sun regrets the error.
WASHINGTON -- Astronomers peering through the Hubble Space Telescope at the core of a giant galaxy 50 million light years from Earth say they have found the first conclusive evidence of the existence of a super-massive "black hole" -- an object with gravity so powerful that it traps everything that comes near, even light.
FOR THE RECORD - CORRECTION
NASA officials yesterday called the discovery Hubble's "most significant so far" and among NASA's most important ever.
As big as two or three billion suns packed into a region as wide as our solar system, the black hole lurks at the core of the M87 galaxy, one of 1,000 galaxies clustered in the constellation Virgo.
"If it isn't a black hole, then I don't know what it is," said Johns
Hopkins University astronomer Holland Ford, who has been pursuing this discovery since 1979. When the conclusive data finally arrived May 5 at the Space Telescope Science Institute in Baltimore, he said, "We were all walking about a foot off the ground. . . . It's finally a lot of fun."
First theorized 30 years ago, black holes are believed to form from the collapsed atomic rubble of stars, dust and gas. Since no light or other signals escape from their gravitational grip, they reveal nothing directly of their nature.
And until Hubble was repaired in December, no telescope has been able to see deep enough into any galaxy to reveal what might lie near its core.
The presence of the black hole in M87 was finally revealed by the speed of hot gas that is swirling toward the galaxy's center, accelerating like suds into a tub drain. Hubble's instruments clocked the gas 60 light years from the center at 1 million miles an hour -- fast enough to cross the U.S. in seven seconds.
(A light year is the distance light travels in one year, or about 5.9 trillion miles. Sixty light years is about four times the distance from the Earth to the nearest star other than the sun, Alpha Centauri.)
Nothing but the gravitational attraction of something at M87's core with a mass of two or three billion suns could prevent matter at that speed from flying off in all directions.
The only candidate within the confines of today's physics that meets that description, the scientists said, is a super-massive black hole.
"This is a tremendous breakthrough," said Daniel Weedman, NASA's director of astrophysics. A longtime black-hole skeptic, he is now a convert.
"I do believe there is a super-massive black hole at the center of [M87]," he said.
A primary goal
Getting proof of the existence of black holes at the cores of galaxies was one of the primary goals established for the Hubble telescope at its launch in April 1990. But its mirror flaw delayed the observations until this year.
In February, barely 30 days after it resumed gathering scientific data, Hubble snapped its first picture of the core of M87. To astronomers' astonishment, it revealed a surprisingly well-ordered, spiraling "pancake" of hot gas -- just what they needed to measure its speed.
On May 5, they got their first speed measurements from Hubble's Faint Object Spectrograph. Gas on one side of the spiral was rushing toward Earth at a million miles an hour; gas on the other side was rushing away at the same speed.
"We nailed it. We knew we had it," said Richard J. Harms, the spectrograph's principal investigator.
Dr. Weedman yesterday called the black hole discovery Hubble's "most significant so far, [and] very close to the top of [NASA's] most significant discoveries."
Hubble scientists will now continue their pursuit. They'll peer deeper into M87 for more data on the black hole there, and into other galaxies to see whether they, too, have black holes at their centers.
Astrophysicists don't know how super-massive black holes are created, or whether they are a cause or effect of giant galaxies like M87. They may form from the merger of smaller black holes.
Although the oldest stars in M87 are nearly as old as the universe itself -- 12 billion to 15 billion years -- Dr. Harms said the age of M87's black hole is unknown.
Its internal structure, if it has any, can never be known because no light or anything else can ever emerge to reveal it.
One structure astronomers can see is a giant, braided jet of hot gas that is spewing from near the center of M87 at right angles to the spiral of inflowing gas.
The fast-moving jet, which emits powerful radio waves and X-rays, is believed to be debris from the destruction of stars entering the black hole.
Ultimate fate unknown
The black hole's ultimate fate is also unknown. Given enough time, it could eventually consume the entire M87 galaxy, and even other galaxies that blunder within range.
"Earth is in no immediate danger," quipped University of Washington astronomer Bruce Margon, who helped design the Faint Object Spectrograph.
While M87's black hole "has an infinite appetite, it can't hunt," said Dr. Harms.
While Hubble's discovery is the best proof yet for the presence of super-massive black holes at the cores of at least some galaxies, earlier evidence had been collected indicating the existence of smaller black holes elsewhere in space.
Astronomers believe they have seen these "stellar mass" black holes indirectly in the behavior of binary or twin stars, in which one extremely small and massive star appears to be drawing matter away from its much larger partner.