When is an exoplanet not an exoplanet? When it’s a white dwarf, of course. Well, at least in the case of KOI-256 (Kepler Object of Interest, number 256).

NASA’s amazing exoplanet hunter, the space-based Kepler mission, spotted an object transiting the red dwarf star, KOI-256, using its standard technique—as the object passes in front of its star, Kepler detects a decrease in the star’s light.

But something looked different about this star. In addition to the dip in brightness from the transiting object, the star’s brightness seemed to vary in a way that suggested it was behaving quite oddly. So Phil Muirhead, of the California Institute of Technology, began to explore further.

Muirhead and colleagues first used a ground-based telescope to get another look. Measuring the star’s radial velocity, they discovered that the red dwarf was wobbling around like a spinning top. Because of this, the scientists suspected the object wasn’t an exoplanet after all, but something much more massive—likely a white dwarf.

A white dwarf is essentially what a dead star leaves behind—a hot cinder, incredibly massive for its size. It “weighs” a lot more than an exoplanet, so Muirhead needed to figure out how much mass exists in the KOI-256 system.

To measure the combined mass of the two objects in the binary pair, the researchers used a technique called gravitational lensing: one of the consequences of Einstein’s general theory of relativity is that gravity bends light, so scientists use gravitational lensing to figure out how much mass is bending (or lensing) light from more distant sources. And while the technique has been utilized to measure the mass of galaxies, it’s the first time it has been used to “weigh” a binary star system. Since we know the approximate mass of a red dwarf, we can then estimate the mass of the companion, which indeed turns out to be a white dwarf.

“This white dwarf is about the size of Earth but [with] the mass of the Sun,” says Muirhead. “It’s so hefty that the red dwarf, though larger in physical size, is circling around the white dwarf.”

The red dwarf orbits the white dwarf in just 1.4 days. This orbital period is so short that at an earlier time the stars must have previously undergone a “common-envelope” phase in which the red dwarf orbited within the outer layers of its companion star—a giant star that eventually died and left behind the white dwarf we see today.

The short orbital period also means the red dwarf’s days are numbered. In a few billion years, the intense gravity of the white dwarf will strip material off the red dwarf, forming a hot accretion disk of in-falling material around the white dwarf.

New Scientist offers an animation of the two stars currently in action (with a rockin’ soundtrack). The research is published in the Astrophysical Journal.

Image: NASA/JPL-Caltech

The galaxy, dubbed with the melodic name MACS 1149-JD, was spotted using  the combined power of NASA’s Spitzer and Hubble space telescopes as well as the phenomenon of gravitational lensing – using the gravity of nearer massive galaxies to bend and magnify the light of more distant ones behind them, which would otherwise remain invisible.

Small and compact, the galaxy appears to contain the equivalent of only about 1 percent of the Milky Way’s mass. The galaxy is quite young, only about 200 million years old, but we see it far back in time, when the Universe was quite young. (Imagine looking at an old photograph of your great grandparents: an old image showing a perhaps quite young couple.)  Light from the young galaxy captured by the orbiting observatories shone forth when the 13.7-billion-year-old Universe was just 500 million years old.

MACS 1149-JD existed during an important era when the Universe began to emerge from the cosmic Dark Ages. During this period, the Universe went from a dark, starless expanse to a recognizable cosmos full of galaxies. The discovery of the faint, small galaxy opens up a window into the deepest, remotest periods of cosmic history.

“This galaxy is the most distant object we have ever observed with high confidence,” says Wei Zheng, lead researcher on a paper appearing in Nature this week. “Future work involving this galaxy—as well as others like it that we hope to find—will allow us to study the universe’s earliest objects and how the Dark Ages ended.”

According to leading cosmological theories, the first galaxies should have started out tiny like MACS 1149-JD. They then progressively merged, eventually accumulating into the sizable galaxies of the more modern universe.

These first galaxies likely played the dominant role in the “epoch of reionization,” the event that signaled the demise of the universe’s dark ages. This epoch began about 400,000 years after the Big Bang when neutral hydrogen gas formed from cooling particles. The first luminous stars and their host galaxies emerged a few hundred million years later. The energy released by these earliest galaxies is thought to have caused the neutral hydrogen strewn throughout the Universe to ionize, or lose an electron, a state that the gas has remained in since that time.

Astronomers plan to study the rise of the first stars and galaxies and the epoch of reionization with the successor to both Hubble and Spitzer, NASA’s James Webb Telescope, which is scheduled for launch in 2018. The newly described distant galaxy likely will be a prime target.

Image: NASA/ESA/STScI/JHU

In broad strokes…  We have dark energy, which makes up 73-74% of the Universe and causes the Universe to accelerate in its expansion. Dark matter, on the other hand, makes up 22-23% of the Universe, accounts for most of the mass and exerts gravitational effects on galaxies—influencing the rotational speed, orbital velocity, and distribution of the remaining 4% of the Universe, namely the stuff we can actually see.

But what if you could see the dark stuff? Would the images match up to the theories describing it?

Scientists at NASA/JPL, working with a West Point mathematician and using the Hubble Space Telescope, have created one of the sharpest maps to date of dark matter.

Focusing on a galaxy cluster called Abell 1689, 2.2 billion light years away, the team was able to create a map of dark matter using gravitational lensing.

Abell 1689 contains about 1,000 galaxies and trillions upon trillions of stars. Its gravitational influence, the majority of which results from dark matter, acts like a cosmic magnifying glass, bending and amplifying light from galaxies much farther away. This effect, called gravitational lensing, produces multiple, warped, and greatly magnified images of those galaxies, like the view in a funhouse mirror. By studying the distorted images, astronomers estimated the amount of dark matter within the cluster. If the cluster’s gravity only came from the visible galaxies, the lensing distortions would be much, much weaker.

Researchers used the observed positions of 135 “lensed” images of 42 background galaxies to calculate the location and amount of dark matter in the cluster. They superimposed a map of these inferred dark matter concentrations, tinted blue here, on a Hubble image of the cluster.

According to team leader Dan Coe, “the lensed images are like a big puzzle. Here we have figured out, for the first time, a way to arrange the mass of Abell 1689 such that it lenses all of these background galaxies to their observed positions.”

The new dark matter observations may yield new insights into the role of dark energy in the Universe’s early formative years.

Will the theories prove correct? From Discover’s Cosmic Variance blog:

We have theoretical predictions about how dark matter should act, and it’s good to compare them to data. Interestingly, the fit to our favorite models is not perfect; this cluster, and a few others like it, are more dense in a central core region than simple theories predict. This is an opportunity to learn something — perhaps clusters started to form earlier in the history of the Universe than we thought, or perhaps there’s something new in the physics of dark matter that we have to start taking into account.

Astronomers will use the new “dark” map to shed light on how the Universe has evolved in the past—and will continue to evolve in the future.

Here’s how it works: When a large nearby object, such as a galaxy, blocks a distant object, such as another galaxy, gravity from the nearby object causes light to detour around it. But instead of taking a single path, light bends around the object sometimes doubling, sometimes quadrupling, sometimes creating an entire ring of light around the nearby galaxy.

Astrophysicist Phil Marshall explains it quite well using a birthday candle and wine glass stem here.

Using the Hubble Space Telescope and WMAP data, the Stanford team could measure the distances light traveled from a bright, active galaxy to the earth along different paths. For example, if the light quadrupled around the nearby object, the scientists could measure it four times, along four separate paths.

Marshall likens it to four cars taking four different routes between places on opposite sides of a large city, such as Stanford University to Lick Observatory, through or around San Jose. And like automobiles facing traffic snarls, light can encounter delays, too.

By understanding the time it took to travel along each path and the effective speeds involved, researchers could infer not just how far away the galaxy lies but also the overall scale of the universe and some details of its expansion.

Using light bent by gravity, astronomers can measure the Universe—a yardstick billions of light years in length!