[This new finding from the NANOGrav team is like adding another
color – gravitational waves – to the picture of the early universe
that is just starting to emerge, in large part thanks to the James
Webb Space Telescope.]
[[link removed]]

SUNDAY SCIENCE: A SUBTLE SYMPHONY OF RIPPLES IN SPACETIME –
ASTRONOMERS USE DEAD STARS TO MEASURE GRAVITATIONAL WAVES PRODUCED BY
ANCIENT BLACK HOLES  
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Chris Impey
June 30, 2023
The Conversation
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_ This new finding from the NANOGrav team is like adding another
color – gravitational waves – to the picture of the early universe
that is just starting to emerge, in large part thanks to the James
Webb Space Telescope. _

Black holes and other massive objects create ripples in spacetime
when they merge., Victor de Schwanburg/Science Photo Library via Getty
Images

 

An international team of astronomers has detected a faint signal
[[link removed]] of gravitational waves
reverberating through the universe. By using dead stars as a giant
network of gravitational wave detectors
[[link removed]],
the collaboration – called NANOGrav [[link removed]] – was
able to measure a low-frequency hum from a chorus of ripples of
spacetime
[[link removed]].

I’m an astronomer
[[link removed]] who
studies and has written about cosmology
[[link removed]], black holes
[[link removed]] and exoplanets
[[link removed]].
I’ve researched the evolution of supermassive black holes
[[link removed]]
using the Hubble Space telescope.

Though members of the team behind this new discovery aren’t yet
certain, they strongly suspect that the background hum of
gravitational waves they measured was caused by countless ancient
merging events of supermassive black holes.

Pulsars are spinning dead stars that emit strong beams of radiation
and can be used as accurate cosmic clocks.

Using dead stars for cosmology

Gravitational waves [[link removed]]
are ripples in spacetime caused by massive accelerating objects.
Albert Einstein predicted their existence in his general theory of
relativity
[[link removed]],
in which he hypothesized that when a gravitational wave passes through
space, it makes the space shrink then expand periodically.

Researchers first detected direct evidence of gravitational waves in
2015, when the Laser Interferometer Gravitational-Wave Observatory,
known as LIGO
[[link removed]],
picked up a signal
[[link removed]]
from a pair of merging black holes
[[link removed]] that had traveled 1.3 billion
light-years to reach Earth.

The NANOGrav collaboration is also trying to detect spacetime ripples,
but on an interstellar scale. The team used pulsars
[[link removed]],
rapidly spinning dead stars that emit a beam of radio emissions.
Pulsars are functionally similar to a lighthouse – as they spin,
their beams can sweep across the Earth at regular intervals
[[link removed]].

The NANOGrav team used pulsars that rotate incredibly fast
[[link removed]] – up to 1,000 times per
second – and these pulses can be timed like the ticking of an
extremely accurate cosmic clock
[[link removed]]. As
gravitational waves sweep past a pulsar at the speed of light, the
waves will very slightly expand and contract the distance between the
pulsar and the Earth, ever so slightly changing the time between the
ticks.

Pulsars are such accurate clocks that it is possible to measure their
ticking with an accuracy to within 100 nanoseconds. That lets
astronomers calculate the distance between a pulsar and Earth to
within 100 feet [[link removed]]
(30 meters). Gravitational waves change the distance between these
pulsars and Earth by tens of miles, making pulsars easily sensitive
enough to detect this effect.

[A giant, white reflecting dish with a receiver.]
[[link removed]]

The NANOGrav team used a number of radio telescopes, including the
Green Bank Telescope in West Virginia, to listen to pulsars for 15
years. NRAO/AUI/NSF
[[link removed]], CC BY
[[link removed]]

Finding a hum within cacophony

The first thing the NANOGrav team had to do was control for the noise
in its cosmic gravitational wave detector
[[link removed]]. This included noise in the
radio receivers
[[link removed]]
it used and subtle astrophysics that affect the behavior of pulsars.
Even accounting for these effects, the team’s approach was not
sensitive enough to detect gravitational waves from individual
supermassive black hole binaries
[[link removed]]. However, it had enough
sensitivity to detect the sum of all the massive black hole mergers
that have occurred anywhere in the universe since the Big Bang – as
many as a million overlapping signals.

In a musical analogy, it is like standing in a busy downtown and
hearing the faint sound of a symphony somewhere in the distance. You
can’t pick out a single instrument because of the noise of the cars
and the people around you, but you can hear the hum of a hundred
instruments. The team had to tease out the signature of this
gravitational wave “background”
[[link removed]]
from other competing signals.

The team was able to detect this symphony by measuring a network of 67
different pulsars for 15 years. If some disruption in the ticking of
one pulsar was due to gravitational waves from the distant universe,
all the pulsars the team was watching would be affected in a similar
way. On June 28, 2023, the team published four papers
[[link removed]]
describing its project and the evidence it found of the gravitational
wave background.

The hum the NANOGrav collaboration found is produced from the merging
of black holes that are billions of times more massive than the Sun.
These black holes spin around one another very slowly and produce
gravitational waves with frequencies of one-billionth of a hertz
[[link removed]].
That means the spacetime ripples have an oscillation every few
decades. This slow oscillation of the wave is the reason the team
needed to rely on the incredibly accurate timekeeping of pulsars.

These gravitational waves are different from the waves LIGO can detect
[[link removed]].
LIGO’s signals are produced when two black holes 10 to 100 times the
mass of the Sun
[[link removed]] merge into one
rapidly spinning object, creating gravitational waves that oscillate
hundreds of times per second.

If you think of black holes as a tuning fork, the smaller the event,
the faster the tuning fork vibrates and the higher the pitch. LIGO
detects gravitational waves that “ring” in the audible range. The
black hole mergers the NANOGrav team has found “ring” with a
frequency billions of times too low to hear.

[A star-filled sky with many spiral galaxies.]
[[link removed]]

The James Webb Space Telescope has allowed astronomers to peer back in
time and study the first galaxies to form after the Big Bang. NASA,
ESA, CSA, STScI
[[link removed]]

Giant black holes in the early universe

Astronomers have long been interested in studying how stars and
galaxies first emerged
[[link removed]]
in the aftermath of the Big Bang. This new finding from the NANOGrav
team is like adding another color – gravitational waves – to the
picture of the early universe that is just starting to emerge, in
large part thanks to the James Webb Space Telescope
[[link removed]].

A major scientific goal of the James Webb Space Telescope
[[link removed]] is to help researchers study how the
first stars and galaxies formed after the Big Bang. To do this, James
Webb was designed to detect the faint light from incredibly distant
stars and galaxies. The farther away an object is, the longer it takes
the light to get to Earth, so James Webb is effectively a time machine
that can peer back over 13.5 billion years to see light from the first
stars and galaxies
[[link removed]] in the
universe.

It has been very successful in the quest, having found hundreds of
galaxies
[[link removed]]
that flooded the universe with light in the first 700 million years
after the big bang. The telescope has also detected the oldest black
hole
[[link removed]]
in the universe, located at the center of a galaxy that formed just
500 million years after the Big Bang.

These findings are challenging existing theories of the evolution of
the universe.

It takes a long time to grow a massive galaxy
[[link removed]].
Astronomers know that supermassive black holes lie at the center of
every galaxy
[[link removed]]
and have mass proportional to their host galaxies. So these ancient
galaxies almost certainly have the correspondingly massive black hole
[[link removed]]
in their centers.

The problem is that the objects James Webb has been finding are far
bigger than current theory says they should be.

These new results from the NANOGrav team emerged from astronomers’
first opportunity to listen to the gravitational waves of the ancient
universe. The findings, while tantalizing, aren’t quite strong
enough to claim a definitive discovery
[[link removed]]. That will likely change,
as the team has expanded its pulsar network to include 115 pulsars
[[link removed]] and should get results from
this next survey around 2025. As James Webb and other research
challenges existing theories of how galaxies evolved, the ability to
study the era after the Big Bang using gravitational waves could be an
invaluable tool.[The Conversation]

Chris Impey [[link removed]],
University Distinguished Professor of Astronomy, _University of
Arizona
[[link removed]]_

This article is republished from The Conversation
[[link removed]] under a Creative Commons license. Read
the original article
[[link removed]].

UNEARTHING CULINARY PASTS—WITH HELP FROM LLAMA POOP
[[link removed]]
A food archaeologist investigates everyday eating and lean times among
the ancient Moche of Peru through a remarkable discovery of thousands
of llama “beans.” Cues to how the Moche survived during times of
drought, conflict, inequality and political collapse.
Sapiens
By Katherine L. Chiou

* Science
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* physics
[[link removed]]
* astronomy
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* gravity
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* Big Bang
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