Following up on our recent discussion of interstellar distances and how they are determined comes word of a reassessment of the distance to the Orion Nebula. The star forming region is famous not only for its beauty but for the opportunity it gives us to assess young stars as they emerge from the interstellar gases around them. Their distance tells us something about their intrinsic brightness and thus their ages.
The change in distance revealed in the new studies is considerable. Whereas the previous best estimate to the Nebula was 1565 light years, the new one, drawn with an uncertainty of six percent, is 1270 light years, a twenty percent adjustment. The Very Long Baseline Array was behind this work, using familiar parallax methods to observe a star called GMR A from opposite sides of Earth’s orbit.
“This measurement is four times more precise than previous distance estimates,” says Geoff Bower (UC-Berkeley). “Because our measurement reduces the distance to this region, it tells us that the stars there are less bright than thought before, and changes the estimates of their ages.”
And what a change. These stars are twice as old as once thought.
What we’re still doing — and we’re early in the process — is getting an approximation of the three-dimensional structure of nearby interstellar space. VLBA is ideal for this work because its ten 25-meter radiotelescope dishes stretch from the Pacific (Hawaii) to the Caribbean (Virgin Islands), allowing it to produce images of remarkably high resolution. Huge amounts of work remain to be done as we adjust distances to various targets. It’s amazing to consider that if we somehow found a way to reach the stars tomorrow, we’d still be faced with the same conundrum experienced by sailors in the 16th Century, the absence of reliable maps.
VLBA has also made observations of star-forming regions in Taurus and Ophiuchus as well as examinations of the Milky Way’s spiral arms and pulsars. With operations managed from Socorro, New Mexico, it’s the world’s largest dedicated, full-time astronomical instrument. The new findings appear as Sandstrom et al., “A Parallactic Distance of 389 +24/-21 parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations,” accepted by The Astrophysical Journal (abstract).