By Oakland L. Childers
Colorado Daily Staff Writer
Thursday, December 10, 1998

CU senior research assistant Bo Reipurth came to Boulder a year ago hoping to take advantage of the excellent conditions that the area offers astronomers like him. The move paid off in a big way.

Reipurth, whose interests lie in the birth of stars, calls himself a "cosmic midwife." He studies these baby stars because they are the building blocks of the universe, and more importantly to him, they offer clues about the formation of our own sun — a normal star in every sense.

"We can't study the sun's birth, but we can study other stars being born, and by inference we can learn how we came to be," said Reipurth, who is affiliated with CU's Center for Astrophysics and Space Astronomy.

Reipurth has been using a giant telescope in Arizona for his recent work. The telescope's four meter-wide mirror has enormous light-gathering ability, making it optimal for viewing the very faint light produced by young stars. The stars he is interested in are less than 100,000 years old—a blink of the eye on the cosmic time scale. Stars like our sun live up to 10 billion years, he said.

One particular area of the sky has a lot of new stars in it, and that is where Reipurth has his telescope pointed. The area is located in the constellation Orion, which rises in the east in the early evening this time of year, Reipurth said.

This area interests Reipurthbecause the stars there are very young and fairly close to the earth, about 1,500 light years away, or the distance light travels in 1,500 years.

"The richest star-forming region is in the belt of Orion," said Reipurth. "In the last 1 million years, 10,000 stars have formed in this region, and therefore this is the region of choice for myself and my colleagues.

Perhaps the most exciting is that the smaller stars are located near a massive star, of a type which leads a short and violent life. This massive star is affecting the smaller stars in a surprising way, Reipurth said.

Reipurth explained that stars in early adulthood use gas and dust to grow larger. That material spins in a disk around the growing star. This disk contains the material from which planets such as Earth form, he said.

Some material spirals in to build the star, and some spirals out away from it. The material moving away from the star is ejected in plumes from both ends of the star.

But the stars forming in the area that Reipurth and his colleagues, including CASA director John Bally, have been studying are affected by the massive star that neighbors them. The large star gives off huge amounts of powerful ultraviolet radiation that wipes away all the material the stars use to grow, essentially stunting the smaller stars' growth, Reipurth said.

But Reipurth's observations have shown that the tiny stars are still able to eject plumes, though only from one side, the one facing away from the larger star.

"These stars, deprived of gas and dust, can still eject jets," said Reipurth, "and that's puzzling because we have always assumed that there is a relation between disks and their jets. Our guess at this point is that there must be some remnant material closest to the star."

Reipurth said he is also perplexed that the plumes only emanate from one side of the stars affected by the massive star.

Reipurth wants to find out if our sun was formed under these sorts of circumstances, in a system of several smaller stars and a large star. The problem he faces is that any stars that may have been formed near our sun are scattered at a great distance from where they formed, he said. To solve this problem, he plans to study meteorites in our solar system. If a massive star ever existed near our sun, it would have exploded long ago, and isotopes from that star will be imbedded in meteorites, he said.

The next step in examining the young stars in Orion will be to look at them with the Hubble Space Telescope, Reipurth said. Last week he secured a time to use the telescope in 1999, to take a very close look at the stars and what is causing them to make the plumes he has discovered.