Sight Unseen: How Astronomers Discover Massive Far-Away Objects

By Erin Biba

Some exciting new techniques to aid sky watchers in detecting new stellar objects.

Astrophysicists at Stanford recently announced they believe the universe is populated by hundreds of thousands of rogue planets. These Nomads were thrown out of their solar systems when they were formed and, with no sun to orbit, are left to roam the galaxy frozen and alone. The realization that these planets are so common is changing the way many think about the formation of planets and the makeup of matter in the universe. No one has ever seen one, but new technologies and telescopes being created over the next decade may change that.

Looking for Light

Though it’s true that no one has ever seen a Nomad directly, astronomers have been able to detect their existence. But how is that possible if these planets are so cold, dark, and far away? They use a technique called Gravitational Microlensing. Predicted by Einstein in the 1930s, it’s only in the last 20 years that sky watchers have been able to perfect the technique. Basically, astronomers are identifying Nomads by looking out for bursts of light. That may seem overly simplistic, but it works. When a planet-sized object passes between earth and a star -- but isn’t close enough to the star to be in orbit around it -- the planet will momentarily act as a lens, amplifying the star’s light, and appearing to us on earth as a short increased burst of light. (Sometimes even doubling the brightness for as much as two minutes.)

Image Credit: NASA

Of course, there’s no way to tell for sure what the object is that’s amplifying the light of a faraway star. “When it comes to figuring out what exactly is doing the lensing, are they really planets? What are they? Of course we don’t understand that in detail. Part of that is because the experiments aren’t that good yet,” says Dimitar Sassalov, a professor of Astronomy at Harvard and Director of the university’s Origins of Life Initiative. But the results of the lensing is provocative enough to nudge scientists to improve their techniques, he says.

That’s the dream of the team at Stanford whose recent research estimated that Nomads are much more common than anyone ever thought. Louis Strigari, an astrophysicist who worked on the research, says the team is hoping astronomers will build a survey mission around the numbers they have published -- and the constraints they demonstrated for the Nomads’ existence (for example, they can’t exert too much gravitational pull because they’re not in orbit).

The Stanford team is hoping to design their own experiment based on their findings over the next decade. But, in the meantime, says Strigari, there are new telescopes that will be coming on line in the next ten or so years that will help solve the problem of seeing the Nomads and answering questions about their existence. Here are some of those telescopes.

New Ways to See the Sky

The New Sky Large Synoptic Survey Telescope, for example, currently undergoing design and development, will be uniquely powerful when its camera clicks on in Chile in the next decade. Thanks to $30 million in funding from donors like Bill Gates, the LSST will have the world’s largest digital camera (3,200 megapixels) and the capability to produce between 20 and 30 terabytes of data nightly. Covering 20,000 square degrees of the southern sky, the LSST will be able to look at the entire sky in just three days. It will also look at every patch of sky it can see about 1,000 times over the course of ten years. And, finally, it will have the ability to trigger almost instant alerts for objects that have changed their position or brightness.

Another mission that may answer questions about Nomads is called GAIA and will be launched next year by the European Space Association. The telescope will fly out past Hubble where it will settle in and survey one percent of the 100 billion stars in our galaxy. The goal is to create a detailed map of our area of space -- looking at each object 100 times and logging changes with each pass. Scientists believe it will be able to see brown dwarfs -- another type of cold dark object that, similar to nomads, are hard to spot because of their lack of heat.

Image Credit: ESA
Image Credit: NASA

Finally, NASA’s Wide-Field Infrared Survey Telescope will take microlensing from the earth’s surface into space. From a position outside our atmosphere, the telescope will have a much better chance at recognizing bursts of light caused by planets smaller than earth (something that is currently very difficult from the ground). With a focus on dark energy science and the discovery of new exoplanets, WFIRST has, likely, the best chance of answering questions about the existence and formation of Nomads.

Regardless of improving technology, astronomers will still have a hard time finding Nomads. As SETI’s senior astronomer Seth Shostak says, “You need to know where to look. We’re light years away. It’s like looking at Highway 101 from space. It’s very hard to find these guys.

But astronomers have always proven to be very clever about making things that are impossible to see visible.” So, while it’s not possible just yet to get a close look at these cold, dark wanderers it’s fair to say that, when it comes to better understanding the universe and how it works all we need is a little time and a lot more fancy technology.