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Friday, 25 April 2008 00:44

First look: Black hole ejects plasma jet

An international group of astronomers used a series of radio telescopes to look at—for the first time—a supermassive black hole ejecting a high-speed jet of plasma particles, what is called a blazar.

A blazar is a supermasive, highly energetic black hole (millions of times more massive than the Sun) centered inside a galaxy that has one or more very compact and highly variable jets pointing in the general direction of Earth. Because the jets are pointing toward Earth, astronomers are able to observe their variability.

Blazars were predicted by astrophysicists to exist. Theoretical models stated that they should have a shape like a twisted corkscrew from a strong magnetic field near the black hole. The magnetic field would accelerate the plasma as it ejected out of the black hole.

However, nobody had actually seen a blazar before—until now.

A black hole is a dense concentration of mass—so dense that nothing can escape its gravitational force that pulls everything inside of it: stars, lights, all matter that comes too close.

However, as in the case of blazars, while mass is gravitationally forced into the black hole, plasma is, as a direct result, ejected out of the black hole at very high velocities.

The jets are sent out in streams of high-energy plasma (supercharged particles) at relativistic speeds—speeds near the speed of light. Some say up to 99.9% of the speed of light.

Because of the extreme amounts of energy coming off of blazars, they are some of the most violent objects known to exist in the universe. However, the ejected plasma is difficult to observe because it is not ejected in a predictable manner.

This group of scientists were lucky enough to actually observe one.

For the first time, astronomers have observed a blazar doing what it does best: throwing out a plasma jet in the direction of Earth. The lead researcher on the team is U.S. astrophysicist Alan Marscher (Institute for Astrophysical Research, Boston University, Massachusetts, United States).

His international team announced their discovery on Wednesday, April 23, 2008.

More details of the important study to astronomy appears on the next page.

The Marscher team used the Very Long Baseline Array (VLBA) at the National Radio Astronomy Observatory (NRAO).

The VLBA is a system of ten radio-telescope antennas, controlled from Socorro, New Mexico—each with a dish of a diameter of 82 feet (25 meters) and weighing 240 tons.

The different radio telescopes within the array are placed over 5,000 miles (8,000 kilometers) apart in the United States, from Mauna Kea on Hawaii; Owen Valley, California; Pie Town, New Mexico; Los Alamos, New Mexico, Kitt Peak, Arizona, and Brewster, Washington, in the western part of the country; to Fort Davis, Texas, and North Liberty, Iowa, in the middle part, to Hancock, New Hampshire and St. Croix in the U.S. Virgin Islands, in the eastern part.

The VLBA website states that its array of radio telescopes provides “…astronomers with the sharpest vision of any telescope on Earth or in space…. the VLBA has an ability to see fine detail equivalent to being able to stand in New York and read a newspaper in Los Angeles.”

The Marscher's team used the VLBA to view the galaxy BL Lacertae (BL Lac), which is located about 950 million light-years from Earth (where one light year is about equal to six trillion miles, or the distance that light travels in a vacuum over a one Earth-year period).

BL Lac is an active galaxy (or active galactic nucleus, AGN), meaning it contains a supermassive black hole at its center. It was the first member of a group of blazar that isnow known as “BL Lacertae objects,” or simply BL Lac objects.

They saw a supermassive black hole with a jet of charged material coming out of it in the shape of a corkscrew—actually, in the shape of a twisted magnetic field.

The team states that the jet originates in the magnetic field near the edge of the black hole. It is within the magnetic field that the particles are accelerated and forced into a jet, or more than one jet.

Actually, during their observation with the VLBA, the researchers saw BL Lac twice eject out a jet. The first time was when the jet was accelerating in speed outward. The second time was when it was considered by the researchers as a "standing shock wave 'farther out in the jet'.” (Smithsonian Institute: “Black Hole Plasma Jet Spotted Tracing Corkscrew Path”]

Marscher stated, "We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated.” [Reuters: “Radio telescopes capture black hole mid-belch”]

The result of the Marscher team appears as an article in the journal Nature.

Marscher says the blazars are, “…one of the most impressive high-energy natural laboratories" in the universe. (Smithsonian Institute: “Black Hole Plasma Jet Spotted Tracing Corkscrew Path”]

And, the conclusion of the team helps astronomers around the world to better understand how black holes accelerate particles outward from itself at near the speed of light.

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