A Jupiter-like planet orbiting a white dwarf hints at our solar system’s future

A glimpse of our solar system’s future has appeared thousands of light-years away in the constellation Sagittarius. There a giant planet like Jupiter orbits a white dwarf, a dim, dense star that once resembled the sun.

In 2010, that star passed in front of a much more distant star. Like a magnifying glass, the white dwarf’s gravity bent the more distant star’s light rays so that they converged on Earth and made the distant star look hundreds of times brighter. A giant planet orbiting the white dwarf star also “microlensed” the distant star’s light, revealing the planet’s presence.

In 2015, 2016 and again in 2018 astrophysicist Joshua Blackman of the University of Tasmania in Hobart, Australia and colleagues pointed the Keck II telescope in Hawaii at the far-off system, which lies some 5,000 to 8,000 light-years from Earth. The team was in search of the giant planet’s star, but saw, well, nothing.

“We expected that we’d see a star similar to the sun,” Blackman says. “And so we spent quite a few years trying to figure out why on Earth we didn’t see the star which we expected to see.”
After failing to detect any light from the spot where the planet’s star should be, Blackman’s team concluded that the object can’t be a typical star like the sun — also known as a main sequence star, which generates energy by converting hydrogen into helium at its center. Instead, the star must be something much fainter. The microlensing data indicate that the star is roughly half as massive as the sun, so the object isn’t massive enough to be a neutron star or black hole. But a white dwarf star fits the bill perfectly, the researchers report online October 13 in Nature.

“They’ve carefully ruled out the other possible lens stars — neutron stars and black holes and main sequence stars and whatnot,” says Ben Zuckerman, an astronomer at UCLA, who was not involved with the work. He notes that only a handful of planets have ever been found orbiting white dwarfs.

The new planet is the first ever discovered that is orbiting a white dwarf and resembles Jupiter in both its mass and its distance from its star. Blackman’s team estimates that the planet is one to two times as massive as Jupiter and probably lies 2.5 to six times farther from the white dwarf star than Earth does from the sun. For comparison, Jupiter is 5.2 times farther out from the sun than Earth is. The white dwarf is somewhat larger than Earth, which means the planet is much bigger than its host star.

The white dwarf formed after a sunlike star expanded and became a red giant star. Then the red giant ejected its outer layers, exposing its hot core. That former core is the white dwarf star.

Our sun will turn into a white dwarf about 7.8 billion years from now, so the new discovery is “a snapshot into the future of our solar system,” Blackman says. As the sun becomes a red giant, it will engulf and destroy its innermost planet, Mercury, and perhaps Venus too. But Mars, Jupiter and more distant planets should survive.

And Earth? No one yet knows what will happen to it.

Speaking out for women in science

Jessica Cantlon
Cognitive neuroscientist
Carnegie Mellon University

Jessica Cantlon, featured in 2016, studies the evolution and development of complex mathematical thinking, including the traits that set humans apart from other primates. In 2017, she was recognized as a Time Person of the Year, as a “silence breaker” speaking out against sexual harassment during the height of the #MeToo movement.

What has been the most notable progress in your research since 2016?
We’ve expanded our repertoire to compare people across different cultures, who have different educational practices. We’ve been going to Bolivia to work with this group of people called the Tsimane, who live in rural parts of the Amazon forest. They don’t have the rigid, formal schooling where kids go through these particular curricula to achieve mathematical cognition. Instead, education there is more organic and more deeply connected to their way of life. That allows us to try to understand what effect does a particular type of education have on numerical thinking.

There was one study that we did, comparing species — nonhuman primates and humans — to understand the evolution of these concepts. Across all species and stages of development and cultural groups, there’s this bias that when you’re looking at a set of objects, and you’re trying to quantify it, you think about that set numerically. And you don’t have to; you can think about that set of objects spatially, as an amount of stuff, you can think about how much surface area is there, or the perimeter around it. But primates, including humans, [tend to] think about that set as a set of discrete objects, and count them up.

What is something that excites you right now in your work?
We’ve looked at the similarities and differences between boys and girls as their brains develop. We’ve done some of the first, early studies comparing children’s brains that can truly allow us to collect evidence on the trajectory of similarity between boys and girls…. We’ve shown that very early in development, between around 3 and 8 years of age, there’s evidence during mathematical processing that most of the brain — over 95 percent — shows functional similarity in that processing between boys and girls.

But as we know, much later on in development, we see a severe underrepresentation of girls in mathematics-related fields. What’s happening? There’s evidence in the field … that what happens in late childhood and adolescence is that children’s interests are shaped culturally.

What are some of the greatest challenges you’ve faced since 2016?
In 2016, [some of my colleagues at the University of Rochester and I] filed a sexual harassment complaint against a faculty member in our department who was sexually harassing women — undergraduate and graduate students and faculty. It became this situation that hijacked my career for a number of years.… We went public with our complaint, partly to protect ourselves, but also partly to let people know at other universities that this kind of thing is happening to students, and it’s affecting women’s career paths in ways that are discriminatory and unequal.

Ultimately, it was really important. Our complaint went public in September of 2017. In October 2017, the Harvey Weinstein story came out in the New York Times, and that kicked off a series of reactions that ultimately culminated in millions of people saying #MeToo, which I think was really powerful and important, and was something that we got to be a part of.

I’ve had dozens of women reach out to me for advice, about how to file a complaint at their university, how to take legal action, if that’s what they’re thinking, what the risks and benefits are. And so, part of my career now — and I’m excited by it, and I think it’s really important work — is to be an advocate for women who are experiencing discrimination and harassment at universities.

One response that we thought was really great was that the National Academies of Sciences, Engineering and Medicine did a full study on sexual harassment in the sciences…. It has a lot of ideas about what might effect larger-scale change.

— Interview by Aina Abell