In the constellation Virgo
Roughly 1 billion times the mass of the Sun
Diameter roughly equal to the size of our solar system
Seen through a decent backyard telescope, 3c273 is a puny sight. It looks like a faint star in the constellation Virgo. Yet that insignificant point of light is the most-distant object visible through most amateur telescopes: about 2.5 billion light-years. The fact that it's visible at all tells us that 3c273 is far from puny. Instead, it is one of the most powerful objects in the universe: a quasar.
3c273 was cataloged in the 1950s as a strong source of radio waves (hence its name: object 273 in the third Cambridge catalog of radio sources). Later, astronomers also discovered a star-like point of light at the same position in the sky. It and several similar objects were described as quasi-stellar objects, which was later shortened to quasar.
When they analyzed the light of 3c273, though, it looked like no other star astronomers had ever seen. The "fingerprints" of various chemical elements found in ordinary stars were nowhere to be found. Instead, the patterns of bright and dark lines in its spectrum appeared to be random and indecipherable.
In February 1963, though, astronomer Maarten Schmidt had a flash of insight. He recognized the patterns of certain elements, but they were drastically offset from their usual position in a spectrum. The patterns were shifted to longer wavelengths, known as a redshift.
A redshift is produced by an object's motion away from Earth; the faster the object is moving, the greater the redshift. The redshift in the spectrum of 3c273 was so severe that it indicated the object was moving away from us at 16 percent of the speed of light -- about 30,000 miles (48,000 km) per second.
Such high-speed motion means that the object is far away, and is moving because of the expansion of the universe itself. A redshift of 16 percent of the speed of light tells us that the object is about 2.5 billion light-years away. For it to be visible from that distance, it must be trillions of times brighter than the Sun! In fact, if it were just 10 parsecs from Earth (33 light-years), 3c273 would shine as brightly in Earth's sky as the Sun does.
That discovery alone was truly remarkable, because no one had ever seen such an energetic object anywhere in the universe. 3c273 was producing many times more energy than an entire galaxy of stars. Yet the story quickly got stranger, because 3c273 was changing brightness over a period of just a few days or weeks. Such rapid change told astronomers that the object must be quite small -- around the size of our own solar system.
And that left astronomers completely baffled. Cramming the energy of an entire galaxy, which can span hundreds of thousands of light-years, into a space that is only a few light-days across, seemed impossible.
As astronomers pondered this conundrum, they eventually came across a remarkable idea: 3c273 and other quasars could be powered by giant accretion disks encircling supermassive black holes. As matter spiraled into such a black hole, it would be heated to billions of degrees. It also would emit energy across the spectrum as electrons spiraled through magnetic fields and as radiation warmed grains of dust in the outer regions of the accretion disk. The model fit the observations perfectly.
So 3c273 consists of a supermassive black hole at the center of an elliptical galaxy. The black hole swallows enough material every year to make a star the size of the Sun, generating enormous energy. It also produces strong jets of charged particles that shoot more than 100,000 light-years away from the black hole. The jets produce energy across the entire spectrum, from radio waves to visible light to X-rays.
The exact mass of the central black hole remains controversial, however. Applying different techniques yields different results. Astronomers have measured the motions of stars around the black hole, the "smearing" of spectral lines by the rotation of the accretion disk, and the brightness of the quasar. Since about 2000, these techniques have yielded estimates ranging from perhaps 10 million to 10 billion times the mass of the Sun. Most methods, however, yield a mass of about one billion times the mass of the Sun.
Whatever its mass, however, the black hole's gravity powers one of the brightest quasars in the universe.
In 2000, Dutch musician Arjen Lucassen released "Universal Migrator Part 2: Flight of the Migrator," a progressive metal album that contains the song "To the Quasar." The song's second movement is about 3c273.
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This document was last modified: March 15, 2012.