I remember once going to a restaurant and, being pretty hungry, ordering the biggest burger on their menu. I grossly overestimated my appetite; what arrived at my table was a ridiculously huge slab of meat, almost impossible for me to finish.
Still, it was a lot smaller than HH 30, a cosmic “hamburger” billions of kilometers in size and weighing about one octillion metric tons. “HH” stands for “Herbig-Haro object,” and the name comes from the astronomers George Herbig and Guillermo Haro, who were the first to closely study these curiously structured, glowing clouds that surround baby stars.
A new image of HH 30 comes courtesy of the James Webb Space Telescope (JWST), which joined forces with the venerable Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) to scrutinize this newly forming star located just 475 light-years from Earth. This is very close, as stars go, so we have a tremendous view of its struggles to be born.
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But our perspective on it is odd, giving rise to the bizarre shape we see. It doesn’t look so much like a star as it does a vast hamburger with a fancy toothpick stuck in it and the condiments sliding off. And lest you think I’m being glib, another nascent star system discovered in 1985 is actually called Gomez’s Hamburger. Astronomers tend to be hungry, and many of us love junk food.
Gastronomy aside, what are we seeing here? The research based on these observations was published by an international team of astronomers in the Astrophysical Journal and looks into HH 30’s structures.
Stars are born in a cloud of gas and dust called a nebula—Latin for “fog,” referring to nebulas’ misty look. Some of these clouds are small, such as Barnard 68, while others are truly immense, such as the Orion Molecular Cloud complex. HH 30 is part of a dark cloud called LDN 1551, a medium-sized nebula in the constellation Taurus that is known to be forming several stars.
Usually a nebula is balanced between being pulled together by its own gravity and being pushed apart by gas pressure. If something happens to tip that balance—perhaps a collision with another nebula or a shockwave passing through from a nearby supernova—the nebula’s gravity can prevail, causing the cloud to collapse.
Material falling onto the center collects and heats up, forming a protostar—an object that can be massive, hot and bright but that doesn’t have enough pressure in its core (yet) to ignite nuclear fusion and shine as a true star. Gas and dust that streams down from farther out doesn’t just fall directly onto a protostar, however. Any small rotation in the material—caused by eddies in the gas, for example—gets amplified as the cloud contracts in much the same way that an ice skater’s spin increases rapidly when they draw their arms in close to their body.
This causes much of the infalling material to flatten out into a so-called accretion disk. The closer in that material is to a central protostar, the faster around the protostar it revolves, giving the swirling gas and dust an outward push via centrifugal force and preventing it from plunging directly in.
This disk can be quite thick and choked with dust—small grains of matter made up of siliceous (rocky) or carbonaceous (sootlike) material. This is opaque to visible light, so if we see that disk edge on, it can block some or all of the protostar’s light. That’s the case with HH 30, creating the patty of the “hamburger.”
The surrounding material—the “bun”—is made of dust and gas above and below the disk that is illuminated by the protostar’s light. This is a reflection nebula (technically a bireflection nebula because there are two of them) and is seen in both the Hubble and JWST observations. That nebula is roughly 90 billion kilometers across, 20 times the distance between Neptune and the sun.
Observations of HH 30 from the James Webb Space Telescope, the Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA).
ESA/Webb, NASA & CSA, Tazaki et al., ESA/Hubble, ALMA (ESO/NAOJ/NRAO) (CC BY 4.0)
This new image, though, shows structures in the nebula that have never been seen before, including a peculiar arc of material that is visible in both the upper and lower sections. It’s not clear what’s causing it. There is some evidence that the protostar here is not a single object but actually a pair, a binary system with the two components orbiting each other fairly close together (separated by about 2.7 billion kilometers, about the same distance between Uranus and the sun). If true, then this binary pair’s orbital dance could be what’s stirring up the disk, creating the arcing spiral. In the new paper, the astronomers propose several other possible mechanisms but also caution that interpretation is difficult; it might turn out to be merely a shadow caused by denser material closer in to the center, an effect like that of the cloud-driven crepuscular rays seen on Earth at sunset.
Then there are those two lighthouselike beams emerging from the top and bottom of the disk. Astronomers call them jets, and they’re very common around still-forming stars (as well as other cosmic objects such as black holes that can sport accretion disks).
It’s not well understood what powers HH 30’s jets, but most theorists suspect very strong magnetic fields are involved. One scenario envisions material from the very inner edge of the disk interacting with the magnetic field of a central, spinning protostar: the magnetic field lines get wound up, a bit like a tornado, which accelerates the material and blasts it out from the protostar’s poles at high speed, creating the oppositely oriented jets. In two images that were taken by JWST about seven months apart, a knot of matter in one of the jets can be witnessed physically moving between the observations, indicating that it’s barreling away from HH 30 at more than 400,000 kilometers per hour!
As for the tail-like structure at the lower left—the “condiments” sliding off—it’s not at all clear what this might be. It may simply be material farther out that was lit by the star, or it might be gas and dust falling toward the star from the surrounding, much larger LDN 1551 cloud.
The ALMA and JWST observations reveal an interesting phenomenon in the nebula. The microscopic dust grains in the cloud come in various sizes, though all are generally on the order of a micron. ALMA is sensitive to light from smaller grains that are about three microns across, while JWST sees bigger grains that are dozens of microns in size. Combining the data from both facilities allowed the astronomers to see size-based sorting of the dust, showing that the larger grains have settled into the opaque disk, while the smaller ones are still well mixed in the upper and lower sections of the nebula. Smaller grains are more easily blown around by the gas in the nebula, so they stay mixed in, while larger ones aren’t, so they settle into the disk.
This might seem a bit esoteric, but it’s actually important. That disk is likely to eventually settle down into a “protoplanetary” phase: the dust gloms together to form larger objects, which stick together to form even bigger ones, eventually giving birth to planets. We don’t fully understand this process—the very same one that created the planet you’re living on—but mapping the peregrinations of differently sized dust grains that are swirling around a forming star could help change that.
Someday the fog will clear, and HH 30 will be seen as a normal star (or two), just another of hundreds of billions in our Milky Way galaxy. And remember, HH 30 now may very well resemble what our own sun looked like when it was being born, some 4.6 billion years ago. Observations like this show us how we came to be, and astronomers are always hungry for more.
