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Neutrino mass, dark energy measurements refined

South Pole Telescope spots cosmic Shadows

The pattern of galactic clusters in the early Universe is helping to reveal the secrets of the neutrino.

Not only that, but astronomers working on South Pole Telescope (SPT) data also hope to yield more information about the dark energy that’s driving the universe apart.

The new results, announced by University of Chicago astronomers at the American Physical Society meeting in Atlanta on April 1, come in the form of a galactic cluster catalogue, among three SPT-based papers just submitted to the Astrophysical Journal.

The 10-meter instrument is designed to operate at the wavelengths of the cosmic background radiation – emitted as light billions of years ago after the Big Bang, but red-shifted down to microwave frequencies by the expansion process.

In the latest analysis, the SPT data has been combined with measurements from X-ray satellite telescopes such as Chandra and XMM-Newton.

Describing the cosmic background radiation as an “image of the universe when it was only 400,000 years old” – before stars and galaxies formed – University of Chicago scientist Bradford Benson said the radiation also reveals the location of distant, massive galactic clusters.

Those clusters, he explained, are helping to reveal both the properties of dark energy, as well as shedding light on the mass range of the (nearly) massless neutrino. They are observable in the cosmic background because of “shadows” left in the radiation as it passed through the clusters.

As the most massive objects in the Universe, galactic clusters “can be effective probes to study physics on the largest scales”, said John Carlstrom, head of the SPT collaboration.

Although neutrinos interact only weakly with normal matter, they are so abundant that that they influenced the number of clusters that formed over the history of the Universe. Hence, by accounting for as many clusters as possible, astronomy helps predict a possible mass range for the particles.

As well as the galactic cluster catalog, the STP data has also yielded a new assessment of the constraints on the cosmological constant (“Einstein’s greatest blunder”), and a measurement of the cosmic microwave background’s angular power spectrum. ®

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