SPACE-TIME RIPPLES: Chinese scientists find key evidence for existence of nanohertz gravitational waves
In
2023, major pulsar timing collaborations across Europe, China, the US
and India jointly released strong evidence for a gravitational wave
background in nanohertz frequencies.
Chinese scientist duo recognized for work in search for space-time ripples
Chinese
researchers have received a prestigious award from the Royal
Astronomical Society for their leading roles in efforts to detect
nanohertz gravitational waves – or ultra-low-frequency ripples in space-time.
Liu
Kuo and Chen Siyuan from the Shanghai Astronomical Observatory (SHAO)
were key contributors to the European Pulsar Timing Array (EPTA)
consortium, which received the society’s group achievement award earlier
this month.
While
working at the Max Planck Institute for Radio Astronomy in Bonn,
Germany, Liu led a team of researchers from Germany, France, Britain,
the Netherlands and other European nations to analyse and release a
major pulsar timing data set in 2023, according to the SHAO.
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The
data, measured to within a billionth of a second, was built on 25 years
of observations from six of the world’s most sensitive radio telescopes.
Pulsars – rapidly spinning neutron stars – serve as cosmic clocks to
reveal the elusive waves through tiny variations in their timing.
Members
of the consortium, which has received the Royal Astronomical Society’s
group achievement award for its work in nanohertz gravitational waves.
Photo: EPTA
Using
this data set, Chen led a team in France at the National Centre for
Scientific Research and the Paris Observatory to search for a faint,
collective signal from pairs of distant supermassive black holes.
His
team successfully identified a signal with a statistical significance
of about three sigma, meaning it was unlikely to be noise. The findings
matched results from other pulsar timing collaborations, SHAO said on
its WeChat account.
“One
of the strengths of the EPTA is its broad, diverse and egalitarian
structure. Involving collaborators of different nationalities and
backgrounds and in particular encouraging and supporting early career
researchers, the EPTA is a model of international and generational
collaboration,” the Royal Astronomical Society said on its website.
Liu
and Chen are now leading efforts to prepare for the next data release
of the International Pulsar Timing Array, which will combine data from
telescopes in Europe, Asia, the United States and beyond. The SHAO said
the goal was to achieve the first definitive detection of nanohertz
gravitational waves within the next few years.
Gravitational waves, first predicted by Albert Einstein’s
general theory of relativity, describe disturbances in space-time that
propagate as waves. In 2015, the Laser Interferometer Gravitational-Wave
Observatory in the US made the first direct detection of gravitational waves in the kilohertz frequency range.
‘Supermassive’ black hole at the centre of our galaxy viewed for the first time
By
contrast, nanohertz gravitational waves are billions of times lower in
frequency, with wavelengths spanning several light years. These waves
are thought to originate from supermassive black hole binaries, cosmic phase transitions in the early universe, and oscillations of cosmic strings.
To detect these elusive signals, scientists
use a unique technique known as pulsar timing arrays. Millisecond
pulsars, which are highly stable and rotate hundreds of times per
second, serve as ultra-precise cosmic clocks.
By
monitoring tiny variations in the arrival times of their signals on
Earth, researchers can detect subtle distortions of space-time caused by
gravitational waves.
By
analysing correlations in the timing data of multiple pulsars,
researchers can construct a galaxy-scale gravitational wave detector –
allowing them to probe cosmic phenomena beyond the reach of traditional telescopes.
In
2023, major pulsar timing collaborations across Europe, China, the US
and India jointly released strong evidence for a gravitational wave
background in nanohertz frequencies.
This
result was recognised with the Frontiers of Science Award at the
International Congress of Basic Science in Beijing in July. Liu and Chen
attended the awarding ceremony at Tsinghua University, representing the
EPTA and the North American Nanohertz Observatory for Gravitational
Waves, respectively.
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