Small red dots in space intrigue astronomers – 10/01/2024 – Science

The power of the James Webb Telescope was put to the test recently, with results that intrigued even scientists.

The telescope detected signs of objects in space that were formed 12 billion years ago, relatively shortly after the Big Bang, which would have occurred 13.8 billion years ago.

These are objects that have never been detected before and that challenge what science knows about how galaxies form.

Because of their brightness in the red spectrum of the instruments used to observe them, astronomers have named the objects “little red dots.” But defining what they are is generating debate among scientists.

They look like small galaxies, about 3% the size of the Milky Way but containing billions of stars.

They could also be galaxies with large numbers of black holes, which is a formation that has never been observed to date in the closest known galaxies.

It all depends on how these astrophysical objects are being observed.

Some experts even compare its change in appearance to a species of octopus that can change its color and shape to camouflage itself.

They are “masters of disguise”, says astrophysicist Fabio Pacucci, from the Smithsonian Institute, in the United States.

Change of appearance

The small red dots “come from such distant distances that they arrive here very weakly”, astronomer Mario Hamuy, professor at the University of Chile, explains to BBC News Mundo.

“They are typically 3,000 light-years in diameter, about 3% of the diameter of the Milky Way, for example, and have a very reddish color, which happens because the light they emit has been strongly changed by the presence of grains of dust around you.”

Unlike household telescopes, large telescopes like the James Webb can capture light from very distant objects in the Universe. The energy signals it receives can be captured at different frequencies, which are analyzed in spectra.

When James Webb focused on the most distant points in the Universe, he came across signs of “little red dots”, which had different characteristics from previously known astrophysical objects.

Depending on how you look at the spectrum, they have characteristics that divide scientists’ opinions.

“All light sources in the Universe change their appearance when you observe them in different windows of the electromagnetic spectrum. In the same way that happens when you make an image with X-rays or with light from your hand. In the first case, you will see the bones of the hand, and in the second you will see the skin”, explains Hamuy.

“The small red dots are no exception. Depending on the spectrum window you use, you will see distinct internal regions of the object,” he says.

Like other objects from the beginning of the Universe, these points existed billions of years ago. Telescopes like the James Webb detect light that has since traveled through space.

Because of these differences in spectrum analysis, scientists saw these small red dots have different characteristics: sometimes like a galaxy that houses millions of stars, sometimes like a galaxy with a supermassive black hole.

“We don’t see this type of galaxies in our nearby Universe. It was something that appeared at this time at the beginning of the Universe, which lasted for a certain time and which now we no longer see”, astrophysicist Begoña Vila, instrument engineer, told BBC News Mundo. from NASA.

“When we started observing them, at first we thought they were another object. But now we know they are galaxies and that is super exciting for everyone.”

Because they are different and because they are “masters of disguise”, the objects are challenging the models that scientists have built to explain the origin of galaxies.

Rethink what we know

What is surprising about these objects, explains Vila, is that it is not known how they could contain so many stars — a number perhaps similar to that of the Milky Way — in such a small space, astronomically speaking.

“How so many stars formed so quickly is anyone’s guess,” he says.

Pacucci explains that in these galaxies there would be so many stars in such a small space that it is as if the entire population of China were placed in one room.

This leads to the question of whether the models that scientists have to explain the formation and composition of galaxies in the early stages of the formation of the universe are correct.

“The models that exist on the formation of galaxies currently explain very well what we have around us, the nearby galaxies. But there are already indications that they need modifications to explain this primordial universe, these galaxies”, says Vela.

Likewise, if the little red dots are actually galaxies with a supermassive black hole, scientists’ understanding of how they form will have to be rethought. But not at a level that alters the great theories, explains Vila.

“(At first) it seemed that cosmology was broken and it was thought that it had to be changed. But it wasn’t like that. The Big Bang is still perfect, there are no problems”, says the NASA expert.

“What happens is that the models we had until now were based on the data we knew and reflected what we knew until now. But it’s clear that this early Universe has surprises and that’s what James Webb was designed for.”

What happens now?

Since the little red dots were identified and their change in appearance was discovered, scientists have continued their studies with new models and instruments to observe them.

It is hoped that in the coming years researchers will have a theory that can explain what they are and how they formed.

For Vila, perhaps the most appropriate answer is not to define whether they are galaxies with millions of stars or supermassive black holes: “It could be a bit of both theories.”

But this will also allow scientists to learn more about the formation of the Universe from phases that —until before the launch of the James Webb Space Telescope— little was known about.

“The most surprising thing is that the little red dots are very abundant. If they were active galaxies, they would outnumber quasars [galáxias muito pesadas] detected by traditional methods by a factor of ten”, says Hamuy.

He adds: “In either scenario, the little red dots are crucial to understanding the early formation of galaxies.”