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Nasa has detected a surprising surplus of infrared light in the dark space between galaxies.

Baffled astronomers say the lights is a diffuse cosmic glow as bright as all known galaxies combined.

They believe it could be from orphaned stars flung out of galaxies.

This artist's concept shows a view of a number of galaxies sitting in huge halos of stars. The stars are too distant to be seen individually and instead are seen as a diffuse glow, colored yellow in this illustration. The CIBER rocket experiment detected this diffuse infrared background glow in the sky and found that the glow between galaxies equals the total amount of infrared light coming from known galaxies.

The findings redefine what scientists think of as galaxies, Nasa said.

Galaxies may not have a set boundary of stars, but instead stretch out to great distances, forming a vast, interconnected sea of stars. 

'We think stars are being scattered out into space during galaxy collisions,' said Michael Zemcov, lead author of a new paper describing the results from the rocket project and an astronomer at the California Institute of Technology (Caltech) and NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. 

'While we have previously observed cases where stars are flung from galaxies in a tidal stream, our new measurement implies this process is widespread.'

Using suborbital sounding rockets, which are smaller than those that carry satellites to space and are ideal for short experiments, the Cosmic Infrared Background Experiment (CIBER) captured wide-field pictures of the cosmic infrared background at two infrared wavelengths shorter than those seen by Spitzer. 

Because our atmosphere itself glows brightly at these particular wavelengths of light, the measurements can only be done from space.

'It is wonderfully exciting for such a small NASA rocket to make such a huge discovery,' said Mike Garcia, program scientist from NASA Headquarters. 

'Sounding rockets are an important element in our balanced toolbox of missions from small to large.'

During the CIBER flights, the cameras launch into space, then snap pictures for about seven minutes before transmitting the data back to Earth. 

The CIBER rocket launch, taken from NASA's Wallops Flight Facility in Virginia in 2013.This photo shows a time-lapse capture of the first three stages of the Black Brant XII class rocket at the time of launch.  It detected a surprising surplus of infrared light in the dark space between galaxies.

Scientists masked out bright stars and galaxies from the pictures and carefully ruled out any light coming from more local sources, such as our own Milky Way galaxy.

 What's left is a map showing fluctuations in the remaining infrared background light, with splotches that are much bigger than individual galaxies. 

The brightness of these fluctuations allows scientists to measure the total amount of background light.

To the surprise of the CIBER team, the maps revealed a dramatic excess of light beyond what comes from the galaxies. 

The data showed that this infrared background light has a blue spectrum, which means it increases in brightness at shorter wavelengths. 

This is evidence the light comes from a previously undetected population of stars between galaxies.

Light from the first galaxies would give a spectrum of colors that is redder than what was seen.

HOW THEY DID IT

The CIBER experiment consists of three instruments, including two spectrometers to determine the brightness of Zodiacal light and measure the cosmic infrared background directly. 

The measurements in the recent publication are made with two wide-field cameras to search for fluctuations in two wavelengths of near infrared light. 

Earth's upper atmosphere glows brightly at the CIBER wavelengths. 

But the measurements can be done in space—avoiding that glow—in just the short amount of time that a suborbital rocket flies above the atmosphere, before descending again back toward the planet.

CIBER flew four missions in all; the paper includes results from the second and third of CIBER's flights, launched in 2010 and 2012 from White Sands Missile Range in New Mexico and recovered afterward by parachute. 

In the flights, the researchers observed the same part of the sky at a different time of year, and swapped the detector arrays as a crosscheck against data artifacts created by the sensors.

This graphic illustrates how the Cosmic Infrared Background Experiment, or CIBER, team measures a diffuse glow of infrared light filling the spaces between galaxies. The glow does not come from any known stars and galaxies; instead, the CIBER data suggest it comes from stars flung out of galaxies. First, sky images are collected via different rocket flights. A small part of a sky image is shown in the left panel. The actual images are 20 times the area of the full moon.

In short, , 'although we designed our experiment to search for emission from first stars and galaxies, that explanation doesn't fit our data very well, Zemcov says

'The best interpretation is that we are seeing light from stars outside of galaxies but in the same dark matter halos. 

'The stars have been stripped from their parent galaxies by gravitational interactions—which we know happens from images of interacting galaxies—and flung out to large distances.' 

Future experiments can test whether stray stars are indeed the source of the infrared cosmic glow. If the stars were tossed out from their parent galaxies, they should still be located in the same vicinity. 

The CIBER team is working on better measurements using more infrared colors to learn how stripping of stars happened over cosmic history.