News & Analysis Physics World  February 2017

New telescope to hunt primordial ‘B-modes’

Looking up The Ngari-1 cosmic microwave background telescope is to be built near the Shiquanhe Observatory in Tibet. (Chinese Academy of Sciences)

Construction has begun on what will be the world’s highest-altitude telescope to study the cosmic microwave background (CMB). The Ngari-1 telescope is to be built at 5250 m above sea level near the Shiquanhe Observatory in the Ali, or Ngari, region of Tibet and is expected to be complete by 2021. It will aim to detect primordial “B-mode” polarization of the CMB – the “curl” of polarized CMB light that is considered to be the smoking gun for cosmic inflation, which occurred about 10–38 s after the Big Bang.

The telescope is a collaboration between the Institute of High Energy Physics (IHEP) in Beijing and Stanford University in the US, which is one of the leading institutions behind the BICEP telescope in Antarctica. In 2014 researchers working on BICEP claimed to have spotted the first evidence for B-modes in the CMB. The claim was later withdrawn when it was shown that the measurement was actually a foreground effect caused by dust within the Milky Way.

Ngari-1 will observe the CMB in the northern sky that telescopes at the South Pole and in the Atacama Desert in Chile cannot see and will operate at 90 and 150 GHz. The telescope will contain thousands of microwave detectors, with the exact number depending on funding and the final design. As China does not currently have the capability to fabricate ultrahigh-frequency, high-sensitivity microwave detectors, Stanford is expected to design and build them.

IHEP has secured about 100 million yuan (£14m) from the Chinese Academy of Sciences for Ngari-1 with the Natural Science Foundation of China granting a “special director’s fund of over 30 million yuan”, according to University of Hong Kong physicist Meng Su, who is a member of the project. The Chinese Ministry of Science and Technology (MOST) may also provide some funding but this has yet to be announced. “If we can receive funding from MOST, we will be able to increase the number of detectors for Ngari-1, that’s important to increasing the sensitivity compared to [BICEP] and provide the opportunity for lower noise per pixel measurement over a large fraction of the northern sky,” adds Su.

Given strict travel controls imposed by the Chinese government, it is difficult for foreigners to travel to the site in Tibet, which has made some question whether the telescope can be built by 2021. Yet the government is supporting that target as it would allow scientists to start observations before Japan launches LiteBIRD – a satellite for detecting primordial B-modes in the CMB that is expected to launch in 2021 and operate for at least three years.

Xin Hao