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| Ultra-distant galaxy from 400 million years after Big Bang points to abundance of dark matter in newborn Universe (image: Nasa, ESA, and L. Infante/Pontifícia Universidad Católica de Chile) |
PETER MOON
Once upon a time, there was a very far-off galaxy, which existed when the Universe was very young, only 400 million years after the Big Bang.
It was a very old galaxy and the farthest away anyone had ever observed. The rays of light it emitted traveled through space for more than 13 billion years, 96% of the age of the Universe, or three times the age of the Solar System, until they were picked up by the Hubble and Spitzer space telescopes.
The distant galaxy was named Tayna, which means “baby” in Aymara, a language spoken in the Andes and Altiplano regions of South America. Analysis of its light showed the galaxy to be very young and massive, compact, and full of giant blue stars. According to the current theory of the Universe’s evolution, the galaxy should not have existed.
It is pointless to argue against facts and images. Tayna should not exist, but it does, so the theory must be wrong – it does indeed appear to need adjusting, according to Alberto Molino Benito, a cosmologist from Madrid who is doing postdoctoral research at the University of São Paulo’s Institute of Astronomy, Geophysics & Atmospheric Sciences (IAG-USP) in Brazil.
Molino is one of the authors of a scientific article about the discovery published in The Astrophysical Journal. His postdoctoral research is supervised by Claudia Mendes de Oliveira, another cosmologist who studies galaxy formation and evolution.
Despite the combined power of Hubble and Spitzer, Tayna is so far away and faint that it is invisible even to those powerful telescopes. “To detect Tayna, our group had to resort to sophisticated techniques such as gravitational lensing,” Molino said.
Albert Einstein predicted phenomena such as gravitational lensing in his General Theory of Relativity.
According to Einstein, the gravitational force exerted by a body with a large mass, such as a galaxy cluster, bends and distorts space around it. This distortion acts like a huge virtual (or gravitational) lens, deflecting and magnifying the light from much more distant objects positioned behind the cluster when it is being observed.
“We combed space for massive galaxy clusters that might act as gravitational lenses to enable us to see objects too faint to be visible normally,” Molino said. They eventually opted for MACS J0416.1-2403, a massive cluster of galaxies located approximately 4 billion light-years from Earth. The cluster weighs as much as a million billion suns. This inconceivably huge mass acts like a zoom lens on a camera, boosting the light from Tayna, which is positioned exactly behind the cluster, to make it look 20 times brighter than normal.
Having detected Tayna, the astronomers had to estimate how far away it is. They did so by studying its light using a tool called “photometric redshift”.
This is how it works: the farther away an astronomical object, the lower the frequency of its light on reaching us, and the redder it becomes. Their estimate by this method showed Tayna to be 13.3 billion light-years from Earth. Its light has traveled all that time before reaching us. This means we can observe Tayna as it was 13.3 billion years ago, when the Universe was only 400 million years old.
Giant blue stars
Light from a distant object tells us not only its location and age but also how far away it is. “Analysis of the light from a galaxy can also show its size and mass, how many stars it contains, and the proportion of young and old stars in this stellar population,” Molino said. “The more bright blue young stars it contains, the younger it is.”
Tayna is full of giant blue stars, very young and bright, and ready to explode into spectacular supernovae before becoming dark holes. As for size, Tayna is comparable to the Large Magellanic Cloud, a diminutive irregular galaxy that is a satellite of our Milky Way.
“Four hundred million years is a very short time for the existence of such a well-formed galaxy,” Molino said. “The most recent models of the Universe’s evolution suggest the first galaxies emerged when it was much older.” By older, Molino meant an adolescent aged approximately 1 billion years, rather than a newborn baby aged only 400 million.
There is only one explanation for the existence of Tayna and the 21 other faint young galaxies the researchers detected near the outer edge of the observable universe. “They could only have formed so soon after the Big Bang if the amount of dark matter in the Universe was larger than we have always thought,” Molino said.
Dark matter makes up 80% of the Universe, corresponding to five times the mass of all 100 billion galaxies in the observable Universe. It is invisible because it emits no light, and we can only detect it from its gravitational effects, so no one knows what it is made of. This is one of the most crucial questions in cosmology today.
There are several theories about the nature of dark matter, but scientists cannot explore it directly because it is invisible. They know it exists thanks to its gravitational action on galaxies. If it were not for dark matter, the galaxies would have shattered long ago. Without dark matter, there would be no Universe as we know it. Perhaps we ourselves would not exist.
“The only explanation for Tayna’s existence and for its being as it was when the Universe was 400 million years old is dark matter, which must have accelerated the clustering of stars together to form the first galaxies,” Molina said. “The more dark matter there is, the faster the galaxies can form.”
It is impossible to discover much more about Tayna and its fellow proto-galaxies in the newborn Universe because the available technology has been used to the limit. “To know more, to see the first galaxies better and infer the action of dark matter, we must wait until 2018, when Hubble’s successor, the next-generation James Webb Space Telescope, will be launched,” Molino said.
The James Webb Space Telescope’s primary mirror will be 6.5 m in diameter, much bigger than the Hubble’s 2.4 m. It will be optimized for longer wavelength coverage and have greatly improved sensitivity. Molino and his colleagues are counting on these future enhancements to continue detecting distant galaxies. They plan to build the world’s largest 3D database on the Universe. “Only then will we be able to confirm how the Universe formed and evolved,” he said.
The article “Young Galaxy Candidates in the Hubble Frontier Fields” by Leopoldo Infante et al., published in The Astrophysical Journal (DOI: 10.1088/0004-637X/815/1/18), can be read at arxiv.org/abs/1510.07084.
Originally published at Agência Fapesp
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