How a Star is Born (and Why We Don’t Know Why)


Giles Novak at the South Pole Giles Novak at the South Pole

If you think summer is ending before it really began this year, you’re not alone. But there’s still time to enjoy one of the season’s simplest and loveliest pleasures – the night sky. We asked Evanston resident and professor of physics and astronomy Giles Novak to help us appreciate what’s up there.

Generally speaking, your research aims to help explain how new stars are born. How are stars born?

It’s a cycle. In our galaxy, we have many stars, billions of them. But there’s also a large amount of gas and dust spread out in the nearly empty spaces between the stars. Gravity works on these clouds of gas and dust (called interstellar clouds) until they begin to move together. Eventually, they collapse under the gravity, and then a whole bunch of stars are born. But stars don’t live forever. They tend to have catastrophic endings and explode into gas and dust. That starts the cycle again.

A key aspect of your work focuses on how long it takes for these clouds of gas and dust to collapse into new stars. Why does this intrigue you?

Based on everything we know, like how to calculate the effects of gravity for example, interstellar clouds should collapse much more often than they do. We should have hundreds of new stars forming in our galaxy each year -- but we only have a few. It’s a mystery. There’s something unknown holding things up so they can’t collapse. Some astronomers think that magnetic fields are holding them in place.

There are different ways to create magnetic fields. One way is simply with a magnet, like the ones on your refrigerator at home. Another way has to do with the motion of vast numbers of electrically charged particles. These magnetic fields are really common. The Earth has one. Stars, like our Sun, have them. And the entire galaxy generates a large scale magnetic field as well. One theory is that this galactic magnetic field is countering the gravity in those interstellar clouds.

We’ve shown that large scale magnetic fields exist in interstellar clouds by using a specialized telescope at the South Pole, where there’s very little water in the atmosphere to interfere with our research. But even the tiny amount of water at the South Pole makes it impossible to measure the strength of the magnetic fields. And we need that to tell if they explain the rate at which new stars are born.

So our next step is to go above the atmosphere. We’re going to put our equipment on a balloon launched by NASA from Antarctica later this year, and point the telescope in various directions to measure, hopefully, the magnetic field strength in interstellar clouds.

Why are you, like many astronomers, also interested in how heavy stars are?

Because it gets toward a very fundamental question. The Sun has a mass in kilograms of 2 with 30 zeros after it. That’s about average for stars, some have 29 zeros, some 31, but most are right around 30. It turns out that’s the mass needed to sustain hydrogen burning for billions of years. But we don’t know why. If we can understand more about the rate at which stars are born, that may help answer a big piece of the puzzle about why the Sun’s mass is just about right to help sustain life on a rock like Earth.

Speaking of Earth, what are some good local places for star gazing and what can we look for in the next few weeks?

There are many beautiful things this time of year that are easy to see. One of the brightest in the whole sky is a star called Vega that is almost directly overhead right after sunset. Next to it is the constellation Cygnus (pronounced sig-nus), the swan. The head of the swan is the star Albireo. With binoculars, it’s easy to see that Albireo is really a beautiful pair of stars. They’re even different colors. And Jupiter, which is just rising at sunset and is highest around midnight is a lovely object to see. Look for its moons with binoculars.

As for local viewing places, there are two ways to go about it. One way is to get a good pair of binoculars or small telescope, a star book from any library or bookstore, and then find a dark sky, which might mean having to get a bit away from the city.

The other way needs no equipment or real travel. Come to Northwestern’s Dearborn Observatory any Friday evening at 9 pm and look through our telescope. It’s free, and there’s someone there to point it and explain what you see.


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