The Heart of a Giant Space Blob
published during a waning gibbous moon.

This rendering shows a snapshot from a cosmological simulation of a Lyman-alpha Blob similar to LAB-1. Credit: ESO

In the great beyond floats a blob of gas. Though color-coded in the image above with tangerine hues and tomato veins, the real hydrogen glob emits ultraviolet light radiation that gave the object its name, the Lyman-alpha Blob, or LAB for short. (But we can all agree calling it a blob is significantly more fun). What powers these rare celestial bodies has been an enigma since their discovery over 15 years ago, but a study published this week revealed what lives at the heart of LABs: feverish, star-rich galaxies.

Astronomers have found dozens of blobs, but one in particular — LAB-1, aka BLOB-1 in this author’s mind — has caught the most attention due to its enormous size. BLOB-1 earns its nickname: It extends across about 300,000 light-years of space.

Though the simulation of the journey to BLOB-1 above is short, the object is a titanic distance from us, because the light that we’re seeing took 11.5 billion years to make it to Earth. The particular wavelength that the blobs emit is called Lyman-alpha radiation, and supercomputer simulations like that of NASA’s Pleiades can show shots of how a body’s gas and dark matter can evolve. The simulated Lyman-alpha Blob image, for instance, shows cold gas (mostly neutral hydrogen) as red, and hot gas is white. If you’re unfamiliar with star formation, it’s a very hot and chaotic process.

Using ALMA (the Atacama Large Millimeter/Submillimeter Array), astronomers watched light from chilled dust clouds to hone in on BLOB-1’s emissions. After comparing notes with the European Space Agency’s Very Large Telescope and the Hubble Space Telescope, they found two galaxies frenetically churning out stars at a rate 100 times that of our own Milky Way.


This diagram explains how a Lyman-alpha Blob, one of the largest and brightest objects in the Universe, shines.

But how does it become so, well, blobby? Basically, the Lyman-alpha photons scatter off the hydrogen gas surrounding the central galaxies and their satellites. “Think of a streetlight on a foggy night — you see the diffuse glow because light is scattering off the tiny water droplets,” lead study author Jim Geach said in a statement. “A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas. The galaxies are illuminating their surroundings.”

The core galaxies might also munch on materials catapulting from other galaxies close by. Researchers hope that the blobs can shed some insight into just how galaxies form, and what states our universe was in every step of its formation.