There is an interesting conversation to be had around naming astrophysical objects. On one hand, we have extremely unique names, such is the word “nebula” or “novae” which have an extensive history.

The same cannot be said for blobs.

Blobs

Lyman-alpha blobs (LABs) are clouds of gas that emit a large portion of light with the Lyman-alpha wavelength (see end of post for more info).

Their discovery was relatively recent (2000) compared to other structures such as nebulae and active galaxies. Because of their newness, fewer than 30 blobs have been discovered so far. The irony is that these humongous structures are some of the oldest in the universe!

Himiko (figure on the right) is likely older than most galaxies for example!

How are they made?

Gas on its own isn’t a source of light in the way that a star is, but one clue as to what’s going on is the gargantuan size of these blobs. LABs are some of the largest single structures in the universe. LAB 1 for example is just under 100kpc, that’s over 3x the width of the Milky Way!

It is likely that active galaxies and other large sources embedded in the blob are heating up the gas, causing it to emit the Lyman-alpha line. TON618 is a good example of this and due to its size it could also be a blob in its own right.

It’s quite difficult to observe through the Lyman-Alpha wavelength. This is because it is in the ultraviolet range of light i.e. the worst bit of the electromagnetic spectrum! Ultraviolet scatters in the atmosphere similarly to blue light, making ground-detection difficult. Not only that, but UV and blue light also suffer from being scattered in space due to dust! Hence, it makes sense why these weren’t discovered until much later.

That being said, I personally think they’re important targets for UV astronomy. Their involvement in the evolution of active galaxies and the fact that they are early universe structures makes them really valuable objects that could hold a lot of key information about a time in the universe that we don’t know much about.

Why are they called “blobs”?

The name “blob” was coined by Steidel et al in their 2000 paper on the objects. It doesn’t seem they were being serious about officially naming them blobs given all the “quotation marks”, I think the name just kinda stuck around because it actually seems to morphologically describe the structures best.

Even funnier, it seems most of the blobs don’t even have a name. Most of the information on blobs are in research papers rather than websites like mine. Maybe I haven’t read enough papers, but every time a new paper talks about a specific blob, they just cite the paper it was discovered in. Kimock et al literally has just a table of papers!

A couple blobs have names such a LAB 1 and Himiko. Himiko in particular might actually be an early galaxy beginning to form given its age and lack of stars.

More on Lyman-Alpha

When an excited electron jumps down an energy level, the difference in energy is released as a photon with a wavelength corresponding to the energy according to Planck’s relation.

Lyman Alpha is the first spectral line people learn because it represents the jump from energy level 2 (first excited state or n=2 ) to level 1 (the ground state or n=1) in Hydrogen.

Lyman Alpha is technically a doublet because of spin-orbit coupling, but if we just treat it as one line we can say that the Lyman Alpha’s wavelength is 121.56 nanometers. This puts it in the ultraviolet range.

The energy of the gap is inversely proportional to wavelength (i.e long wavelength = low energy), so in the diagram on the right, a bigger energy gap (bigger arrow) means a bigger energy, which is a smaller wavelength.

Here’s my references and ways to learn more:

Giant Space Blob Glows from Within

More information on LAB 1 can be found from this paper by Bower et al.

The original paper by Steidel et al which showcased the discovery of the blobs.

The Origin and Evolution of Lyman-alpha Blobs in Cosmological Galaxy Formation Simulations by Kimock et al.

More information on Himiko and the paper marking its discovery by Ouchi et al.

CHANDRA’s website on LABS.