Our Universe in 3D

More astronomers than ever are gathering in National Harbor, Maryland—right now! The 245th meeting of the American Astronomical Society (AAS) kicked off Monday, and several announcements at the meeting focused on how astronomers figure out the three-dimensional nature of the Universe.

Because objects in the Universe are incredibly distant—and we look at the sky from our perspective on Earth—we essentially see everything as two-dimensional. Except that we know very well we live in a complex, three-dimensional Universe that requires some effort to tease apart.

So how do astronomers do that?

For some objects, it’s relatively straightforward. A planetary nebula results from the outer layers of a star expanding into space at the end of its life. If you know where the center of expansion is, you can reconstruct the shape of the planetary nebula based on the motion of the material moving away from its center. You just need to measure the speed of the stuff.

And it turns out that it’s relatively straightforward to measure the speed of some molecules. Carbon monoxide, for example, emits a very specific and easily identifiable wavelength of light, and because of what’s known as the Doppler shift, we can tell how quickly a carbon monoxide molecule is moving toward us or away from us.

That’s the basic technique used by Joel Kastner of the Rochester Institute of Technology. He and his team looked at the Ring Nebula—a popular target for astronomers since the first image of it was taken in 1886. A photo is intrinsically two-dimensional, though, and the structure of the Ring Nebula has been a hot topic for astronomers since, well, probably that first photo.

Kastner and his team have reconstructed a three-dimensional view of the nebula that should put some of the debate to rest. As the press release notes, “Astronomers have theorized that the nebula is ring-shaped or has a soap bubble structure, but the model created from the SMA data revealed it is an ellipsoid.”

David Rupke from Rhodes College presented recent work on a galaxy his team named Makani, the Hawaiian word for wind in honor of the research done at Maunakea on the Big Island of Hawaiʻi. (An article about his earlier research describes the object beautifully.)

The wind from Makani isn’t exactly a gentle tropical breeze, however. Instead, it consists of hot gas (about 300,000 Kelvins) flowing away from the central galaxy and seeding the surrounding intergalactic medium with elements. Rupke’s new research underscores how energetic this process is.

Another, somewhat more complicated method for exploring the third dimension in space is to use light echoes as a means of determining the structure of something that reflects light. The term is apt, since it’s a bit like a bat using echolocation to figure out its surroundings.

For example, a supernova that exploded hundreds of years ago emitted light in all directions—including directly toward Earth. Some of the light took a more circuitous route, however, traveling away from Earth and then bouncing off clouds of gas much farther away. Some of the light, reflected off those clouds of gas, is only reaching us now.

Jacob Jencson of Caltech and the Infrared Processing Center (IPAC) led a team of astronomers who used the James Webb Space Telescope (JWST) to map these light echoes in infrared light. Their goal is to tease out the complex shape of potentially star-forming gas clouds lit by the supernova.

Because a consequence of observing light echoes is that if we watch that same reflective region over an extended period of time, we’ll see light bouncing off different parts of a complex cloud structure. The supernova probably only brightened for a week or two, so the pulse of light it created is traveling through space, illuminating what’s in its path. By making repeated observations, astronomers can reconstruct a complicated model, a bit like a medical CT scan.

A different group used a similar technique to figure out what’s going on around the supermassive black hole at the center of the Milky Way (you can read about supermassive black holes in my article from Monday this week). Researchers from the University of Connecticut mapped out gas clouds using flare-ups from our galaxy’s central black hole as sources of illumination instead of the one-off flash of a supernova—and they observed in x-rays instead of infrared light.

They leveraged two decades’ worth of data from the Chandra X-ray Observatory (you can read about that mission in my article from Tuesday this week) to learn about the distribution of gas in two regions dubbed “sticks” and “stones,” but they were also studying the source of the radiation to make sense of the black holes’ history of outbursts.

This is just a smattering of stories from this year’s AAS meeting. Unfortunately, this is my last update for the website from this meeting, but next Thursday, I’ll be presenting “Universe Update” in Morrison Planetarium (simulcast for Academy members) at 6:30 p.m., and I’ll be highlighting stories from AAS—along with some spectacular 3D visualization!