They may not look like much, but six red objects could change our understanding of galaxies in the early Universe — if astronomers are correct.

An international team of astronomers, led by Ivo Labbé of Swinburne University, analysed data captured by the James Webb Space Telescope (JWST) last year.

Their analysis, reported today in the journal Nature, suggests the red objects could be unusually massive galaxies packed full of bright stars that appeared 500–700 million years after the Big Bang.

"That's 10 to 100 times bigger than typical galaxies [in the early Universe] are supposed to be," Dr Labbé said.

If their measurements are right, the masses of the galaxies would be up to​ 10 billion times that of our Sun, with one of them possibly containing as many stars as our present-day Milky Way galaxy (100 billion), but jammed into a size 30 times smaller.

To exist so early in time, these bright galaxies must have grown much faster and been much more efficient than current theories of galaxy evolution suggest.

"You essentially would need to turn all the available gas in the Universe into stars at 100 per cent efficiency to build galaxies this massive, and we know 100 per cent efficiency is impossible," Dr Labbé said.

The hunt for missing galaxies

Astronomers have been hunting for bright galaxies in the early Universe since the Hubble Space Telescope detected "corpses" of fully grown galaxies that existed 1.5 billion years after the Big Bang.

The detection of these dead galaxies, which no longer produce stars, suggests something must have existed earlier.

"The stellar ages of these [dead] galaxies suggest they must have formed earlier, but Hubble has never been able to see them while they were forming," Dr Labbé explained. 

While Hubble Space Telescope is limited to how much of the early cosmos it can see, the JWST uses infrared light to detect objects further back in time and space.

To hunt for the missing galaxies, Dr Labbé and his team used a technique known as photometry to measure the mass of the red objects in the JWST images.

As the Universe expands, light from distant objects shifts to wavelengths towards the red end of the spectrum known as red shift.

And the redder an object is, the denser or more massive it is.

The team found 13 objects: six were very red, indicating they were likely to be massive, while the other seven were low-mass.

However, the data still needs to be confirmed using another technique known as spectrometry, which breaks up the light into wavelengths and gives a more precise measurement of distance.

Galaxies or shining black holes? 

Recently, three of the 13 objects have been studied using spectroscopy by other teams.

Those studies confirmed the distance and mass of two of the low-mass galaxies identified by Dr Labbé's team.

"It is an encouraging sign that spectra confirmed what we had determined from the images using our standard techniques," he said.

The independent studies also looked at one of the six massive objects Dr Labbé 's team is focusing on.

It turned out to be a quasar — bright gas falling into a supermassive black hole at the centre of a galaxy — 12.8 billion light years away (closer than the 13.0–13.2 billion light years estimated by Dr Labbe's team).

"So we're basically discovering a whole new class of objects in the early Universe."

The discovery of a quasar so far away provides a glimpse into how supermassive black holes, which lie in the centre of large galaxies, formed in the early Universe.

"We know that [glowing super massive black holes are] really important because they may influence the evolution of galaxies. They may actually make them stop growing."

Because quasars are some of the brightest objects in the Universe, Dr Labbé said it was hard to work out how much light was coming from the black hole versus stars.

This makes measuring the galaxy using standard techniques difficult, but the galaxy itself could still be massive, he said.

"So one down, five to go," he said.

Dr Labbé and his team plan to study the other objects using the JWST's NIRSpec camera over the next year.

He predicted the five remaining high-mass objects would probably turn out to be a mix of galaxies and early quasars.

A sign of what is to come?

Astrophysicist Robin Cook of the University of Western Australia said it was too early to make any definitive conclusions, but the study was a sign of what was to come.

"In order to confirm a lot of their findings, they really need the spectroscopic follow-ups of these galaxies," commented Dr Cook, who studies galaxy formation but was not involved in this research.

The problem, he said, would be if the distance measurements were incorrect and the objects were much closer.

"The only reason they're claiming them to be so massive is because it seems like they are really, really far away so in order to produce that amount of light they must be really massive," he said.

But, while still "skeptical", Dr Cook said the study used two different signatures to constrain the red shift "which is the best approach you can take" using standard methods.

He said many previous studies claiming massive bright galaxies from early data released by JWST, and since proved incorrect, had just used one.

"You have a much better chance of getting to the correct distance if you find both of these regions exactly where you expect them to be."

And, he added, identifying these potential candidates was important groundwork.

"Spectroscopy is so expensive and it takes so much time so you don't want to point at random patch of the sky and just hope for the best, you really need to develop this this list of candidates."

None of which, he added, would have been possible to detect outside of the JWST era.