Radio Astronomy Reveals a Long and Winding Road in Space

Wow!  Check out this latest image of the Orion Nebula!

Just when you think astronomy can’t get any cooler, something like this comes out: radio astronomers using the Green Bank Telescope (a radio telescope in West Virginia) have found filaments of star-forming gas near the Orion Nebula. Embedded in those filaments are what they think could be large grains of rocky material, the building blocks of planets.

If this discovery is held up through further observations, it would be the first time large particles — perhaps the size of a Lego-type building block — have been detected in such a dense super-nurturing star- and planet-forming nursery. Prior to this, regions of star birth were understood to be thick with dust-sized grains.  The existence of larger grains could change the dynamic of planet formation in this and other regions where larger particles exist.

Scott Schnee, an astronomer at the National Radio Astronomy Observatory (NRAO) and lead on the team doing the work, pointed out that the availability of large-enough (pebble or Lego-sized) planetary building blocks would encourage the formation of planets around newborn stars in the region. “If you want to build a house, it’s best to start with bricks rather than gravel,” he said, implying that it would lead to faster building rates than normal.

Planet formation, similar to building a house, needs material to get started. Most planet nurseries start out with grains of material perhaps no larger than dust specks or maybe sand bits. Over time, those materials stick together to form larger and larger planetesimals, which collide to form planets. If you can start with bigger pieces, that might shorten the planet formation time.

The Orion Nebula is a great place to look for evidence of planet-forming materials because it is long known as a starbirth nursery. The latest GBT observations cover much of the northern part of the Orion Molecular Cloud complex, where the Orion Nebula lies. Within this area, the star-forming material (clouds of gas and rocky grains) have formed long loops that are very rich in the dusty elements needed to form planets.

If you take a closer look at the loops (right), you can see brighter areas within them. Astronomers call these cores, which are the early coalescing forms of what will become stars. There are a great many of them, which means that this area will eventually form a lovely star cluster — perhaps in a few hundred thousand to a million years.

The streams themselves are swarming with particles that could be up to the size of a Lego-style building blocks. That’s somewhat unusual for a young star-forming region, which usually contains much smaller particles of rocky material. Which leads to the question: why does this place have larger-than-usual grains?

There are two schools of thought about the answer. One is that the filaments are just thick enough that they provide the right environment for such particles to grow quickly from dust-size grains to pebbles. The temperatures within these streams are colder than the surrounding nebula and the particles within them move at slower speeds. That would lead to the formation of larger grains. The other idea is that these larger particles could have grown around earlier protostellar cores, or maybe were part of protoplanetary disks — the large disks of gas and dust where planets form around newborn stars. They somehow escaped their earlier birthplaces and are now going through a second round of grown in the streamers.

So, how did astronomers use radio astronomy techniques to find this long and winding road of possible star and planetary formation? Materials in these regions emit and/or radiate light at certain radio frequencies. The GBT focused on an area that had previously been studied by a Spanish 30-meter telescope called IRAM, which is sensitive to emissions measured in millimeter wavelengths. Based on that facility’s data, the astronomers then looked at the same region with the GBT at slightly longer wavelengths. They found that it was much brighter in that region of the spectrum, which means that the material in the loops has different properties (temperature, size, velocity) from the types of interstellar dust normally seen in a star-forming region.

Now that they’ve uncovered this fascinating evidence for bigger planetary building blocks, the team of astronomers involved in this study will make more measurements of these fascinating loops to understand what’s going on in what they poetically call this “pebbled pathway to planet formation.” Stay tuned!