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By Eric Johnson

November 5, 2024—When I interviewed Dr. Jason Xavier Prochaska last Sunday, he was a little jetlagged, having returned from Spain the previous day. While there, he told me, he spent some time studying oceanography. That was a surprise.

Dr. Prochaska, who goes by Xavier and is also known as Dr. X, is a professor of Astronomy & Astrophysics at UC Santa Cruz, and an Astronomer at the University of California Observatories. At UCSC’s Inter[Stellar+Galactic] Medium Program of Studies (IMPS), he is engaged in research into “the nature of gas both within and outside of galaxies, primarily during the first few billion years of the universe.”

Oceanography is a new interest.

With all of that, the talk that Prochaska delivered at the Santa Cruz Museum of Natural History on Wednesday, Oct. 30, was on another topic. Titled “Things That Go Bump in the Night!,” the lecture dealt with the following questions: “If a star consumes another star, and no one is around to hear it, does it make a sound? Have you ever wondered what sound a black hole makes? What about a supernova?”

The event was part of the museum’s Naturalist Night series, which Ross Johnson, the museum’s inspired Public Programs manager, has blown up into something like a cross between a cocktail party and a game show—with charcuterie-and-cheese boards, subject-themed drinks (provided by Santa Cruz’s own Venus Spirits), and audience-participation segments including a science-lecture version of bingo. Johnson himself serves as master of ceremonies (and master of inventive-yet-shameless puns).

Dr. X, in addition to his vast array of interests and disciplines, is something of a historian of the contributions to his science by astronomers in California, in particular in Santa Cruz. We discussed a handful of mind blowing concepts in the current field, and their roots to his fellow Californians. These include, as you will see, the work of Heber Curtis of UC Santa Cruz’s Lick Observatory, whose theories helped give birth to the discovery of the expanding universe and the existence of dark energy.

This conversation has been edited for length and clarity.

The field of astronomy appears to have exploded over recent years, and it seems that the things we know today are far beyond the things I learned in Astro 101 decades ago.

That's true. Especially cosmology and astrophysics. One of the most obvious ones is exoplanets—when I started, not a single planet was known beyond the solar system. Full stop. And now we know thousands. And that whole field has been launched in the last 30 years.

When I started off at that time, people were chatting about dark matter—and while it was on the books, and favored as a real thing, very little was understood. And with galaxies—we knew almost none. Now they're a dime a dozen .

It's a data-driven field, so underneath all of this has been advances in technology—everything from larger telescopes, X-ray and gamma ray telescopes, radio telescopes, to the introduction of high-quality detectors within your phone. Investment in technology has driven 90 percent of those advances.

When I was a kid I read a book on the history of the telescope, and it was a great way to learn astronomy—because as new telescopes were invented, new discoveries were made.

Yes. And one thing I like to harp on—let me raise a hobby-horse here: Being in California—for now more than half of my life—that is our history as well. The Lick Observatory was the first mountain-top observatory, and it blew the field wide open.

We should be respectful to non-white cultures—I'm sure there were ancient cultures that had what we call observatories on mountain tops, but what we today view as a professional mountain-top telescope, Lick was the first. And the observatory has been part of that heritage of advancing discoveries with major new facilities.

That was my next question—the role the Lick Observatory played in advancing the field. Can you talk about an early discovery that was made at Lick?

It would’ve started with stellar astrophysics. In 1886, we didn’t even have galaxies as a concept — that took almost another 40 years. And that came about through what was called the Shapely Curtis debate—[Harlow] Shapely was at Mount Wilson, in Los Angeles] and [Heber] Curtis was up here.

If I showed you the images they were analyzing, you could tell it’s a galaxy, because we’ve all been taught to see them. But in those days they were debating: Is it a large system of stars like our own, at some unimaginable distance, as Curtis claimed? Or is it some other smaller phenomenon within our own galaxy? [Shapley’s position.]

Ultimately, it was Edwin Hubble who took an image at Mt.Wilson—not very precise, but precise enough to form a distance estimate—and he showed that Andromeda, our closest galaxy, had to be well beyond the Milky Way. That proved pretty conclusively that Andromeda must therefore be its own galaxy. And that launched cosmology in the sense we now know it.

What about today? What is being studied at the Lick Observatory now?

We have four professional telescopes, one of which is dedicated entirely to detecting supernova — exploding stars. It’s been doing that for quite a while, and was at the forefront 15 or 20 years ago. We have another dedicated entirely to finding exoplanets — the automated planetary finder, and that’s a leading facility. And then we have two general purpose telescopes, a three-meter and the 40-inch Nickel. The Nickel does mainly imaging, and the three-meter leads some of the development in adaptive optics technology, which is the technique we use to mitigate the blurring of the atmosphere.

What is your work at Lick, and what scientific topics are you interested in these days?

I’m most focused on transient fast radio bursts. These are pulses of radiation from a source that we’re not all that sure about yet. They are detected by nearly all radio telescopes these days, and our team at Santa Cruz does the follow up work—so we identify the galaxy they were admitted from and study their properties. And then we do measurements related to cosmology and the cosmic web — the phenomena which is really why I got involved in the first place.

Can you tell me, what is the cosmic web?

We think there’s a third major component to the cosmos, in addition to mass and energy, called dark energy—which is a silly name, but the one we’ve gone with. And the cosmic web is kind of a colloquial term used to describe the structure or morphology of the universe on large scales.

And this is mainly prediction, although there’s good data, too. So we take a large supercomputer, write code to describe the physics of gravity, and what dark energy would do, and run it forward. And then you can make predictions for how the structure looks on a very large scale. And, the punchline: It looks like a Web. So the galaxies are kind of like nodes where the threads of the web intersect. And there’s other entities—threads—that connect these nodes of the web where the galaxies reside.

So you’re saying the threads that connect the galaxies — that’s not theoretical, these are real?

Well—it’s somewhere in between.

I want to bring this back to Santa Cruz. Beyond what we already discussed, what role have astronomers and astrophysicists here played in studying things like dark matter and dark energy?

Some of the earliest and best theory work was done by three of our faculty—Sandy Faber, Joel Primack, and George Blumenthal. They wrote a seminal paper in the early ’90s that was theoretically driven and motivated by data as well. On the supernova side, one of our current faculty, Ryan Foley, works in that area quite a bit. And then in astrophysics, myself and Piero Madau are using the deep spectra of quasars and their light, which intersects with the cosmic web and kind of illuminates it in silhouette.

Well, obviously, we are going to have to have another conversation about all of that at another time—as well as your new interest in oceanography!

To learn more about the human connection with the stars, visit the Santa Cruz Museum of Natural History’s Out of this World: Looking to the Stars exhibit on display through November 17, 2024. There are also two related Naturalist Night events coming up: UAVs & AUVs from Deep Sea to Deep Space on Nov. 7 and Exploring the Abyss with the E/V Nautilus on November 13. Find all the great upcoming events here!