Baby stars cry loudest

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Oh man, do I love me some Herbig-Haro Objects.

There are two main reasons, and a bunch of littler ones. One of the main ones? They’re absolutely spectacular and beautiful!

That’s a Hubble Space Telescope image of HH 1/2 — literally, Herbig-Haro 1 and 2 — located about a degree south of the Orion Nebula in the sky and at roughly the same distance of about 1,200 light-years away. As semi-abstract art, it’s just incredible.

The ESA Hubble Flickr page has a huge version of this that’s 4,300 x 3,000 pixels in size, so go ahead and download that and peruse it while your jaw hangs agape.

But the science, oh yes the science.

Herbig-Haro Objects (or HHOs) were discovered in the 1800s, but it wasn’t until the mid-20th century that they were understood to be phenomena associated with very young stars. They’re commonly seen in dense nebulae — gas clouds — where stars are being born, which is a big hint. They vaguely resemble Q-tips: A pair of long, thin streams racing away from a central star, with big puffy clouds of gas at the ends. They can easily reach several light-years in length (a light-year is ten trillion kilometers, so wow).

So what creates them?

Stars are born from gas clouds. If a local clump of material becomes dense enough for its own gravity to dominate, it can collapse into itself. This could happen if the wind from a nearby star or supernova hits the nebula, for example, compressing it. As the clump collapses the center gets denser and denser. It will also start to spin to conserve angular momentum; as I’ve written before (about black holes but the principle is the same): “But material almost never falls straight in; it always has some sideways velocity, like water spinning around a drain. As the material flows in that spin increases — we call this conservation of angular momentum, and it's the same reason an ice skater’s spin increases as they bring their arms in.”

The material that gets close to the center experiences a pretty decent centrifugal force outward, which flattens it into a disk called the circumstellar disk, literally the disk around a star. The protostar in the center gets pretty hot, because a lot of material is falling onto it — think of how much heat and energy is given off by a big asteroid impact on a planet, and multiply that by a bazillion — hot enough to heat the disk. The atoms of gas in the disk get so energized they lose their electrons, becoming ionized, technically called a plasma.

This means the gas is now electrically charged, and when you fling around charges like that you generate a magnetic field. Close in to the star that magnetic field lines get wound up tighter and tighter, and at some point the tension is so high that something’s gotta give. Right near the star the field lines erupt outward, twin vortices up and down away from the disk like invisible tornados. But the material itself wants to flow along those magnetic field lines, so that stuff gets accelerated by the magnetic field and flung away.

And it’s flung away hard: The material in HH 1/2 is moving away from the central star at speeds of over a million kilometers per hour! That’s fast enough to get from the Earth to the Moon in about 20 minutes. Yegads.

The magnetic field wraps around that material, keeping it tightly focused into twin beams. However, there’s a lot of gas still floating around near the star, and those beams are plowing through it. After some distance, usually ten trillion kilometers or so, they lose enough energy by slamming into that stuff that the material slows, the magnetic fields weaken, and the material is no longer constrained. It suddenly puffs out, forming the swabs at the ends of the cosmic Q-tip.

The central star of HH 1/2 is hidden behind a thick cocoon of gas in the center, but you can see the beam to the upper right pretty clearly in the Hubble image. The red star on top of the beam (in the image above) is coincidentally placed; it was thought for a while to be the source of the beam but inspection of this high-resolution image shows why that can’t be the case. Along the beam you can see little arcs, like waves off the bow of a boat. That’s what they are; material in the beams slamming into material between the stars, pushing it aside. But you can see the arcs are pointed toward that red star, not away, so that part of the beam must be moving toward the star, and therefore can’t be flung away from it.

That beam and puffy cloud make up HH 1. The cloud to the lower left is HH 2. I think the beam in HH 2 is hidden behind more of that thick material, but the puffy cloud is obvious enough.

This image is a combination of a great many observations taken in different filters, ranging from ultraviolet to infrared. The filters pick out light from different elements like hydrogen, oxygen, magnesium, and sulfur. These all react differently when hit by powerful shock waves, so they emit light differently as they ram through the interstellar material, and that allows astronomers to measures things like their densities and temperatures, which helps them better understand the physics of Herbig-Haro objects. The infrared observations were also taken because at some point JWST will be pointed at this object, and by then the arc-shaped clumps will have moved slightly. That will help more with the physics as well as allow their speeds to be more accurately determined.

That part amazes me too: We can see the motion of these objects even though they’re 24,000 trillion kilometers away! But they’re moving so fast we can see that motion over just a few years. In fact, my friend Judy Schmidt, who is a genius at processing Hubble images, made this animation of HH 47 showing its expansion:

WHOA. She also processed the HH 1/2 observations using different methods and colors than the Hubble image above. There’s obviously a ton of science in these images, but how they get displayed in this way is as much art as science, and different people do it in different ways.

Mind you, I’m barely scraping the surface of the science behind these images, which we now know to be extremely complex — everything involving magnetic fields is a nightmare to understand mathematically and physically. But that does bring me to another reason I love Herbig-Haro Objects so much:

They’re the birth cries of stars. And that wail is loud.

Et alia

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