The James Space Telescope recently observed tiny reddish objects believed to have been created in the early universe. These small objects have been nicknamed “little red dots” (LRDs). Although some initially believed them to be mature galaxies, new analyses suggest that at least some of them are “black hole stars,” i.e., black holes surrounded by a giant sphere of gas that makes them shine like stars.
The James Webb Space Telescope
The James Webb Space Telescope does not observe things like a regular camera that we would have on our cell phones. Instead, it observes the universe in infrared. By observing only the “heat” of things, it can see through the dust of the universe to very ancient times (more than 13.3 billion light-years away).
LRDs are not red because of their light, but because they are redshifted by the expansion of the universe. They are also enveloped in gas and dust. Thanks to key instruments such as NIRCam (images) and NIRSpec (spectra), we can see this.
From what NASA scientists have been able to verify about these LRDs, it appears that they began to exist between ~0.5 and 1.6 billion years after the Big Bang.
If these were normal galaxies filled with old stars, these small red dots would be too bright for such an early stage of the cosmos. They would have to form stars at a rate so fast that we have never observed before, at least near our galaxy. This is why scientists call the little red dots “universe breakers”; they challenge what we once believed was possible for our universe. In short, they are objects that do not fit with our current understanding of galaxy formation.
Black hole stars
LRDs are essentially supermassive black holes surrounded by a giant layer of gas that makes them glow from the heat of the black hole. This is not nuclear fusion like our sun, but rather the glow comes from matter falling in and releasing energy. The gaseous layer covering this black hole hides the signals from active nuclei and at the same time mimics the light of a compact galaxy of red stars. However, this black hole is not composed of these red stars as we believed until now.
This layer of gas causes the black hole to grow faster and faster, becoming more enormous in less than 1 billion years (which is a very short period of time when we consider the age of our universe).
Some alternative hypotheses
Not all LRDs are the same: some galaxies are very dusty with bursts of star formation. On the other hand, some have very weak and compact active nuclei, which make them remain partially hidden. The latter are more difficult to find, even with infrared cameras. To continue studying this, the James Webb Space Telescope will continue to point its X-rays in that direction to find out how many LRDs there are and how they are distributed across the age of the universe.
This new discovery by James Webb solves two problems at once: it explains the brightness of LDCs without resorting to impossible galaxies, while also offering a mechanism by which black holes are able to grow very quickly. The only thing we know is that textbooks will have to be rewritten to explain in an updated way how the first galaxies can arise and when massive black holes appear.
For now, astronaut and scientists alike will continue to investigate these small red dots to learn more about growth rates. The JWST not only takes beautiful photos, but is also rewriting how we conceive of the universe and all the formations within it. Could you have imagined that the beginning of the universe would be so interesting?