A Star Is Born: Celestial Beacon Sheds New Light on Stellar Nursery

A timely discovery by American amateur astronomer
Jay McNeil, followed immediately by observations at
the Gemini Observatory, has provided a rare glimpse
into the slow, yet violent birth of a star about 1,500
light-years away. The resulting findings reveal some
of the strongest stellar winds ever detected around
an embryonic Sun-like star.

McNeil’s find was completely serendipitous. He was
surveying the sky in January from his backyard in
rural Kentucky and taking electronic images through
his 3-inch (8-centimeter) telescope. When he
examined his work, he noticed a small glowing
smudge of light in the constellation of Orion that
wasn’t there before. “I knew this part of the sky very
well and I couldn’t believe what I was seeing,” said
McNeil. Astronomers were alerted almost
immediately, via the Internet, and quickly realized that
he had come across something special.

“It is extremely rare that we have an opportunity to
study an important event like this, where a newly
born star erupts and sheds light on its otherwise
dark stellar nursery,” said Gemini astronomer Dr.
Colin Aspin. Dr. Aspin and Dr. Bo Reipurth, (of the
University of Hawaii’s Institute for Astronomy),
published the first paper on this object, now known
as McNeil’s Nebula. Their work, based on
observations using the Frederick C. Gillett Gemini
North Telescope on Mauna Kea, is in press for the
Astrophysical Journal Letters.

“McNeil’s Nebula is allowing us to add another
important piece to the puzzle of the long, protracted
birth of a star,” said Reipurth. “It has been more than
thirty years since anything similar has been seen, so
for the first time, we have an opportunity to study
such an event with modern instrumentation like that
available at Gemini.”

Detailed images and spectra of the stellar newborn,
taken using the Gemini Near-Infrared Imager and
Multi-Object Spectrograph, demonstrate that the star
has brightened considerably. It is blasting gas away
from itself at speeds of more than 600 kilometers
per second (over 2000 times faster than a typical
commercial airplane). The observations indicate that the
eruption was triggered by complex interactions in a
rotating disk of gas and dust around the star. For
reasons that are still not fully understood, the inner
part of the disk begins to heat up, causing the gases
to glow. At the same time, some gas funnels along
magnetic field lines onto the surface of the star,
creating very bright hot spots and causing the star to
grow. The eruption also cleared out some of the dust
and gas surrounding the young star, allowing light to
escape and illuminate a cone-shaped cavity carved
out by previous eruptions into the gas.

The birth of a star takes several tens of thousands of
years and these observations are but a brief
snapshot of the process. Although this is a very rapid
schedule on astronomical time scales, Reipurth
explained that it’s impossibly slow compared to a
human lifetime. “We astronomers therefore have no
choice but to compare various objects where each
one is in a different state of development,” he said.
“This is very similar to the imaginary situation of an
alien landing on Earth with only half an hour to
understand the full life cycle of humans. By looking at
people of various ages and using some logic, this
alien could piece together our growth from infant to
old age. This is how we are beginning to understand
the birth and youth of stars. Rare events like the one
McNeil discovered help to fill in the blanks in our
understanding of stellar origins.”

This outburst may not be the first time the star has
flared during its long tumultuous birth. Following
McNeil’s discovery, an inspection of archival photographic
plates revealed that a similar event took place in 1966,
when the star flared and faded again into its
enshrouding gas. “We know so little about these
kinds of eruptions that we cannot even say whether
the star will continue to flare or will rapidly fade from
view again,” said Aspin. “We were extremely
fortunate that Mr. McNeil discovered this when he
did. In an event like this, the earlier we can observe
it, the better our chances are of understanding what
is going on.”

Fortunately for Aspin and Reipurth, McNeil
discovered this in the early winter while the Orion
region was still high in the night-time sky. It was also
fortunate that McNeil was so familiar with this part of
the sky that he noticed right away that something had
changed. This combination of circumstances
enabled the astronomers to prepare an observation
run on Gemini very quickly. “Our window for
observing this object is closing rapidly but it will
become visible again later this year,” said Aspin. “By
then this eruption could be over.”

A striking color image from Gemini reveals fine
details in McNeil’s Nebula. The star and its bright
disk shine like a lighthouse through the cavity of gas
and dust. A full-resolution Gemini image of the
nebula and an artist=92s conception of how the
escaping gas and hotspots on a young star might
have caused this event can be found at:
http://www.gemini.edu/media/images_2004-6.html