NASA has discovered an unprecedentedly large cluster of black holes in our nearest galactic neighbor, Andromeda.

The 26 black hole candidates were spotted with the Chandra X-ray Observatory from more than 150 observations spread over 13 years.

Each of the black holes is of the kind that forms after a star collapses in on itself. As they suck in material from other stars that orbit or pass nearby, they also suck in material that gives out X-rays as it is consumed. It's this that Chandra spotted.

To filter Andromeda's black holes from other X-ray sources—such as neutron stars, or much larger black holes much farther away than Andromeda—the astrophysicists had to look for attributes like brightness, variability and color.

These black holes are more easily spotted than most because they have companion stars to provide the material that emits X-rays. "While we are excited to find so many black holes in Andromeda, we think it's just the tip of the iceberg," said Robin Barnard of the Harvard-Smithsonian Centre for Astrophysics, lead author of the study published in The Astrophysical Journal. "Most black holes won't have close companions and will be invisible to us."

The 26 black holes join a previous group of nine found using Chandra data. They are close to Andromeda's "central bulge," the spherical network of huge, old stars that is at the heart of most galaxies.

Andromeda's bulge is larger than the Milky Way's, and that larger number of stars means there is also a corresponding greater number of black holes for us to spot.

Here's a space-age idea if you've ever heard one: NASA is building a galactic GPS system that will provide astronauts a better, more accurate map through our solar system. This is obviously an ambitious undertaking, one that will take generations, not years, to complete.

As Jason Mitchell, an engineer on the project as NASA's Goddard Space Flight Center, explained to IEEE Spectrum, the new system "will allow our descendants to accurately and autonomously navigate not only throughout the solar system but beyond it as well." Mitchell explained that the further we travel from Earth, the less sense our current system makes. "Maybe in the future, when we’re exploring space regularly, we won’t need to rely on a gigantic, Earth-based infrastructure," he said.

If astronauts aren't relying on technology back home, though, then where do they turn? The stars of course. That's right, just like swashbucklers sailing the Seven Seas and nomads wandering the desert, this new super advanced system draws on the same basic principles of navigation that have been in use for millenia. There is a futuristic component that sets it apart from the Antikythera mechanism, though, and it involves pulsars.

Traditionally, space navigation depends on radio waves being beamed from Earth out to the space craft. This is time-consuming since radio waves only travel so fast, and it's also limiting since the craft is almost literally tethered to Earth by the signal. The new system, however, is fully autonomous. Rather than relay messages themselves, the space crews will look to pulsars, zombie stars that blink at regular intervals, to serve as points of reference. The pulsars work a lot like lighthouses, the pretty things in Maine and elsewhere that have long kept ships from running into shore in areas of low visibility.

It wouldn't be quite right to think of pulsars as blinking lights that astronauts could spot outside of portholes. (See above for the sort of cyberpunk effect that is a blinking pulsar.) But again, this is the future, and some futuristic methods are necessarily. IEEE Spectrum explains the workflow:

A craft heading into space would carry a detector that, similarly to a GPS receiver, would accept X-rays from multiple pulsars and use them to resolve its location. These detectors—called XNAV receivers—would sense X-ray photons in the pulsars’ sweeping light. For each of four or more pulsars, the receiver would collect multiple X-ray photons and build a “light curve.” The peak in each light curve would be tagged with a precise time. The timing of these peaks with respect to one another would change as you traveled through the solar system, drawing nearer to the source of some and farther from others. From this pattern of peaks, the spacecraft could calculate its position.

Got that? You can compare the system to lighthouses or you could compare it to the sonar navigation systems on submarines. Either way, it's pretty amazing. [IEEE Spectrum via PopSci]