Hubble Basks in the Glare of a Cosmic Rocket
NASA's Hubble Space Telescope spots a pyrotechnic display that will put any Fourth of July fireworks display to shame. Herbig-Haro 110 (HH 110), a geyser of hot gas in Orion, is splashing up against and ricocheting from the dense core of a molecular cloud.
Herbig-Haro objects are nebulae observed near forming stars. Although they are found in a wide array of shapes, the basics stay the same: twin jets of heated gas shoot off in opposite directions away from a newborn star. These outflows stream through space, stretching out to scales so gargantuan that they dwarf our solar system more than a thousand times over.
When these energetic jets run into colder gas, the collision plays out like a traffic jam on the interstate. Gas within the shock front slows to a crawl, but more mass piles up as the jet continues to slam into the shock from behind. Temperatures skyrocket, and this curving, flared region glows brightly. These "bow shocks" are so named because they resemble the waves that form at the front of a boat.
In the case of the HH 110 jet, astronomers observe an unusual permutation on this basic model. Careful study has repeatedly failed to find the source star driving HH 110, which also lacks a counter-jet pointing in the opposite direction. But there may be good reason for this: perhaps the HH 110 outflow is itself generated by another jet.
Astronomers now believe that the nearby HH 270 jet grazes an immovable obstacle — a much denser, colder molecular cloud core — and caroms off at about a 60-degree angle. The jet goes dark and then reemerges, having reinvented itself as HH 110.
The ridges inside HH 110 show that these stellar fireworks are produced like the erratic outbursts from a Roman candle. As fast-moving blobs of gas catch up and collide with slower blobs downstream, new shock fronts arise along the jet's interior. Emission from hot, excited gas causes these inner boundaries to glow.
The exact way HH jets are launched is still a mystery, but the outline is known — at least in broad strokes. As a disk of leftover material rotates around a newborn star, friction within the spinning disk causes particles to slowly spiral inward. Upon reaching the disk's innermost rim, the infalling gas hops onto magnetic field lines connected to the star. Slow-moving gas can latch onto lines that lead to the star's poles, but gas particles with more angular momentum are banished for their impatience. These faster particles are exiled to interstellar space along magnetic field lines that at first point radially away from the star, and then slowly curve upwards into streams that flow perpendicular to the disk.
This stunning view of the HH 110 jet combines data from Hubble's Advanced Camera for Surveys and the Wide Field Camera 3.
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)