Hunting for gravitational waves from monster black holes

Date:
April 7, 2022
Source:
NASA/Goddard Space Flight Center
Summary:
Our universe is a chaotic sea of ripples in space-time called
gravitational waves. Astronomers think waves from orbiting pairs
of supermassive black holes in distant galaxies are light-years
long and have been trying to observe them for decades, and now
they're one step.



FULL STORY ==========================================================================
Our universe is a chaotic sea of ripples in space-time called
gravitational waves. Astronomers think waves from orbiting pairs of supermassive black holes in distant galaxies are light-years long and
have been trying to observe them for decades, and now they're one step
closer thanks to NASA's Fermi Gamma-ray Space Telescope.


========================================================================== Fermi detects gamma rays, the highest-energy form of light. An
international team of scientists examined over a decade of Fermi data
collected from pulsars, rapidly rotating cores of stars that exploded
as supernovae. They looked for slight variations in the arrival time of
gamma rays from these pulsars, changes which could have been caused by
the light passing through gravitational waves on the way to Earth. But
they didn't find any.

While no waves were detected, the analysis shows that, with more
observations, these waves may be within Fermi's reach.

"We kind of surprised ourselves when we discovered Fermi could help
us hunt for long gravitational waves," said Matthew Kerr, a research
physicist at the U.S.

Naval Research Laboratory in Washington. "It's new to the fray --
radio studies have been doing similar searches for years. But Fermi and
gamma rays have some special characteristics that together make them a
very powerful tool in this investigation." The results of the study,
co-led by Kerr and Aditya Parthasarathy, a researcher at the Max Planck Institute for Radio Astronomy in Bonn, Germany, were published online
by the journal Science on April 7.

When massive objects accelerate, they produce gravitational waves
traveling at light speed. The ground-based Laser Interferometer
Gravitational Wave Observatory -- which first detected gravitational
waves in 2015 -- can sense ripples tens to hundreds of miles long from
crest to crest, which roll past Earth in just fractions of a second. The upcoming space-based Laser Interferometer Space Antenna will pick up
waves millions to billions of miles long.



==========================================================================
Kerr and his team are searching for waves that are light-years,
or trillions of miles, long and take years to pass Earth. These long
ripples are part of the gravitational wave background, a random sea
of waves generated in part by pairs of supermassive black holes in the
centers of merged galaxies across the universe.

To find them, scientists need galaxy-sized detectors called pulsar
timing arrays. These arrays use specific sets of millisecond pulsars,
which rotate as fast as blender blades. Millisecond pulsars sweep beams
of radiation, from radio to gamma rays, past our line of sight, appearing
to pulse with incredible regularity -- like cosmic clocks.

As long gravitational waves pass between one of these pulsars and Earth,
they delay or advance the light arrival time by billionths of a second. By looking for a specific pattern of pulse variations among pulsars of an
array, scientists expect they can reveal gravitational waves rolling
past them.

Radio astronomers have been using pulsar timing arrays for decades,
and their observations are the most sensitive to these gravitational
waves. But interstellar effects complicate the analysis of radio
data. Space is speckled with stray electrons. Across light-years, their
effects combine to bend the trajectory of radio waves. This alters the
arrival times of pulses at different frequencies. Gamma rays don't suffer
from these complications, providing both a complementary probe and an independent confirmation of the radio results.

"The Fermi results are already 30% as good as the radio pulsar timing
arrays when it comes to potentially detecting the gravitational wave background," Parthasarathy said. "With another five years of pulsar data collection and analysis, it'll be equally capable with the added bonus
of not having to worry about all those stray electrons." Within the next decade, both radio and gamma-ray astronomers expect to reach sensitivities
that will allow them to pick up gravitational waves from orbiting pairs
of monster black holes.

"Fermi's unprecedented ability to precisely time the arrival of gamma
rays and its wide field of view make this measurement possible," said
Judith Racusin, Fermi deputy project scientist at NASA's Goddard Space
Flight Center in Greenbelt, Maryland. "Since it launched, the mission
has consistently surprised us with new information about the gamma-ray
sky. We're all looking forward to the next amazing discovery."

========================================================================== Story Source: Materials provided by
NASA/Goddard_Space_Flight_Center. Original written by Jeanette
Kazmierczak. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Ripple_in_space-time ========================================================================== Journal Reference:
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Link to news story: https://www.sciencedaily.com/releases/2022/04/220407145450.htm

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