Washington: For the first time, astronomers have discovered star-like bodies known as brown dwarfs with temperatures that can be even cooler than the human body.

Brown dwarfs, also called Y dwarfs and failed stars, are the coldest objects which are nearly impossible to see relying on visible light.

But with infrared vision of NASA's WISE space telescope, researchers detected the faint glow of six Y dwarfs relatively close to our sun, within a distance of about 40 light-years.

They are too puny to force atoms to fuse together and release nuclear energy, and so they have only the little heat they were born with. This heat fades over time until all the light they do emit is at infrared wavelengths. So far, WISE has detected 100 new brown dwarfs, Live Science reported.

To see how cool the coldest of these six Y dwarfs was, the researchers used NASA's Hubble Space Telescope to analyse its pattern of light.

They found the coldest Y dwarf, known as WISE 1828+2650, was colder than 80 degrees Fahrenheit (25C), less than the temperature of a human body.

The closest of these Y dwarfs, WISE 1541-2250, is nine light-years distant. In comparison, the alien star closest to us, Proxima Centauri, is about four light-years away.

"Finding brown dwarfs near our sun is like discovering there's a hidden house on your block that you didn't know about," said astronomer Michael Cushing, a WISE team member at NASA's Jet Propulsion Laboratory in Pasadena.

"It's thrilling to me to know we've got neighbours out there yet to be discovered. With WISE, we may even find a brown dwarf closer to us than our closest known star," said Cushing, who led the study on the Y dwarfs published in the Astrophysical Journal.

According to the scientists, the coldest brown dwarfs found until now were the T dwarfs, which get as cool as about 440 degrees Fahrenheit (225 degrees Celsius).

First uncovered in sizable numbers in the late 1990s, the dwarfs led astronomers to ask whether there could be dwarfs even cooler.

Scientists name stars and brown dwarfs based on their temperatures, "with 'O' stars being the hottest, and now 'Y' dwarfs being the coldest", Cushing explained.

"Since Y comes after T, we felt it was the appropriate choice. Using Y also leaves room for an additional 'Z' class if astronomers discover even colder objects."

Better understanding Y dwarfs could shed light on how stars and planets form.

"Brown dwarfs in general, and Y dwarfs specifically, are a wonderful bridge between stellar and planetary astrophysics, because we think brown dwarfs form like stars, but in many respects look more like gas giant planets like Jupiter," said Cushing.

"So when we study Y dwarfs, we are not only learning about stars, but also about the conditions of gas giant exoplanets," he added.