Hubble shows mystery object in new light

larger   In the top Hubble photo, jets pulse from both sides of an object known as He2-90. (The diagonal light streaks are optical effects of the telescope.) In the bottom Hubble image, a large dark disk vertically bisects the mysterious bright light

By Richard Stenger
CNN.com Writer

(CNN) -- A young star with pulsing jets? A burnt cinder with a death shroud? Astronomers investigating a bizarre object 8,000 light years away once thought it could be both. Now they wonder if it is neither.

Once classified as a nebula, or the glowing remains of a dying star, the mystery in the constellation Centaurus displays characteristics of both age and youth.

A bright hot cloud enshrouds the object, typical of a nebula. But it also is ringed by a dark, dusty disk and shoots out regular salvos of gas, indicative of an embryonic star.

"We've never seen jets like this in dying star systems. You see jets like this in young star systems or the center of galaxies with black holes in them," said Raghvendra Sahai, lead author of a report published this month in the Astrophysical Journal Letters.

INTERACTIVE Cult 3D model of Hubble Space Telescope     MESSAGE BOARD Stargazing     ALSO Animation of a binary star with jets, one scenario that could explain the He2-90 mystery

Sahai and his colleagues suspect the enigma is neither young nor single.

"Our best guess is that it is a binary system, two stars orbiting each other. We think both stars are very old, one being a red giant, the other a white dwarf," said Sahai, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

They theorize that the red giant, swelling up in its death throes, sheds matter that is captured by the gravity of its smaller companion, a white dwarf, the collapsed remnant of a medium-sized star.

The material swirls into a disk, which about once a century ejects a pair of gaseous pulses in opposite directions. The jets travel at least 375,000 miles (600,000 km) an hour.

Impressive numbers, but surprisingly slow by astrophysical standards, said Sahai, leaving the true nature of the object known as He2-90 still a mystery. The estimated rate of speed could be incorrect or the red giant companion could prove to be a black hole or neutron star, as suggested by an observation by the Compton X-ray Observatory.

"These were just the discovery images. We need to get more data," Sahai said.

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Space Telescope Science Institute
Hubble Heritage Project
Hubble SM3A

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