Lyman-alpha blob — Safekipedia Adventurer

In astronomy, a Lyman-alpha blob (LAB) is a huge cloud of gas that shines in a special way called the Lyman-alpha emission line. These blobs are some of the biggest objects we know of in the Universe. Some of them are bigger than 400,000 light years—much larger than our own Milky Way galaxy, which is about 87,400 light years wide.

The giant Lyman-alpha blob LAB-1 (left) and an artist's impression of what it might look like if viewed from relatively close (right).

Scientists have found Lyman-alpha blobs only very far away in space. This is because the blobs are faint and their light changes to longer wavelengths. This change, called redshift, lets their light reach Earth's atmosphere, which usually blocks this type of light. Because of this, we can only study these blobs when their light has stretched to longer wavelengths.

The most famous Lyman-alpha blobs were found in the year 2000 by a group of scientists. Later, more were found using the powerful Subaru Telescope in Japan. These blobs form a structure that stretches over 200 million light-years. Scientists are still learning how these huge clouds of gas connect to the galaxies around them and what makes them glow so brightly. Studying Lyman-alpha blobs may help us understand how galaxies formed in the early universe.

Examples

Composite of two different images taken with the FORS instrument on the Very Large Telescope of the Lyman-alpha blob LAB-1 in the constellation of Aquarius. Credit ESO/M. Hayes.

Some famous examples of Lyman-alpha blobs include Himiko, LAB-1, and EQ J221734.0+001701, known as the SSA22 Protocluster. Another example is TON 618, a very bright object in space that is powered by one of the most massive black holes known. These blobs are some of the largest single objects ever seen in the universe.