Owens Valley Radio Observatory, together with w. m. keck observatory, is providing new clues in an ongoing cosmic mystery. Credit: Caltech/Ovro/G. Hallinan
Maunakea, Hawaii – Fast radio bursts (FRBs) are
among the most enigmatic and powerful events in the cosmos. Around 80 of
these events—intensely bright millisecond-long bursts of radio waves
coming from beyond our galaxy—have been witnessed so far but their
causes remain unknown.
In a rare feat, researchers at Caltech’s Owens Valley Radio
Observatory (OVRO) have now caught a new burst, called FRB 190523, and,
together with the W. M. Keck Observatory in Hawaii, have pinpointed its origins
to a galaxy 7.9 billion light-years away. Identifying the galaxies from which
these radio bursts erupt is a critical step toward solving the mystery of what
triggers them.
Finding the host galaxies of FRBs is not easy. Before this new
discovery, only one other burst, called FRB 121102, had been localized to a
host galaxy. FRB 121102 was reported in 2014 and then later, in 2017, was
pinpointed to a galaxy lying 3 billion light-years away. Recently, a second
localized FRB was announced on June 27, 2019. Called FRB 180924, this burst was
discovered by a team using the Australian Square Kilometer Array Pathfinder and
traced to a galaxy about 4 billion light-years away.
FRB 121102 was easiest to find because it continues to burst
every few weeks. Most FRBs, however—including the Australian and OVRO
finds—just go off once, making the job of finding their host galaxies harder.
“Finding the locations of the one-off FRBs is challenging
because it requires a radio telescope that can both discover these extremely
short events and locate them with the resolving power of a mile-wide radio
dish,” says Vikram Ravi, a new assistant professor of astronomy at Caltech
who works with the radio telescopes at OVRO, which is situated east of the
Sierra Nevada mountains in California.
The team then conducted follow-up observations using Keck
Observatory’s Low Resolution Imaging Spectrometer (LRIS) to determine the
properties of FRB 190523’s host galaxy.
The LRIS data revealed that the host galaxy for FRB 190523 is
similar to our Milky Way. This is a surprise because the previously located FRB
121102 originates from a dwarf galaxy that is forming stars more than a hundred
times faster than the Milky Way.
“This finding tells us that every galaxy, even a
run-of-the-mill galaxy like our Milky Way, can generate an FRB,” says
Ravi.
The discovery also suggests that a leading theory for what
causes FRBs—the eruption of plasma from young, highly magnetic neutron stars,
or magnetars—may need to be rethought.
“The theory that FRBs come from magnetars was developed in
part because the earlier FRB 121102 came from an active star-forming
environment, where young magnetars can be formed in the supernovae of massive
stars,” says Ravi. “But the host galaxy of FRB 190523 is more mellow
in comparison. “
The Deep Synoptic Array ten-antenna prototype (DSA-10) searches for fast
radio bursts within a sky-area the size of 150 full moons (left).
Within this area, the DSA-10 can locate these bursts with immense
resolving power, isolating them to regions containing just one galaxy
(middle). This feat was achieved for the fast radio burst called FRB
190523, detected by DSA-10 on May 23, 2019. The right panel shows the
time profile of the burst above its radio spectrum. Credit:
Caltech/OVRO/V. Ravi
Ultimately, to solve the mystery of FRBs, astronomers hope to
uncover more examples of their host galaxies.
“With the full Deep Synoptic Array, we are going to find
and localize FRBs every few days,” says Gregg Hallinan, the director of OVRO and a
professor of astronomy at Caltech. “This is an exciting time for FRB
discoveries.”
“We’re
very excited about the new capabilities to find these enigmatic bursts and we
look forward to continuing to provide the critical follow-up data that tell us
how distant these objects are and what environments they live in,” says John
O’Meara, chief scientist at Keck Observatory.
The researchers also say that FRBs can be used to study the amount
and distribution of matter in our universe, which will tell us more
about the environments in which galaxies form and evolve. As radio waves
from FRBs head toward Earth, intervening matter causes some of the
wavelengths to travel faster than others; the wavelengths become
dispersed in the same way that a prism spreads apart light into a
rainbow. The amount of dispersion tells astronomers exactly how much
matter there is between the FRB sources and Earth.
“Most matter in the universe is diffuse, hot, and outside
of galaxies,” says Ravi. “This state of matter, although not ‘dark,’
is difficult to observe directly. However, its effects are clearly imprinted on
every FRB, including the one we detected at such a great distance.”
The Nature study, titled, “A fast
radio burst localized to a massive galaxy,” was funded by NSF and Caltech.
Other Caltech authors include: Morgan Catha, electronics engineer at OVRO;
Larry D’Addario, system engineer; George Djorgovski, professor of astronomy;
Richard Hobbs, software developer at OVRO; Jonathon Kocz, digital research
engineer; Shri Kulkarni, the George Ellery Hale Professor of Astronomy and
Planetary Science; Jun Shi, postdoctoral scholar; Harish Vedantham, a former
postdoctoral scholar now at ASTRON, the Netherlands Institute for Radio
Astronomy;
Sandy Weinreb, visiting associate in astronomy; and David Woody,
assistant director of OVRO.
Source: W.M. Keck Observatory
About LRIS
The Low Resolution Imaging Spectrometer (LRIS) is a very
versatile visible-wavelength imaging and spectroscopy instrument commissioned
in 1993 and operating at the Cassegrain focus of Keck I. Since it has been
commissioned it has seen two major upgrades to further enhance its
capabilities: addition of a second, blue arm optimized for shorter wavelengths
of light; and the installation of detectors that are much more sensitive at the
longest (red)wavelengths. Each arm is optimized for the wavelengths it
covers. This large range of wavelength coverage, combined with the
instrument’s high sensitivity, allows the study of everything from comets
(which have interesting features in the ultraviolet part of the spectrum), to
the blue light from star formation, to the red light of very distant
objects. LRIS also records the spectra of up to 50 objects simultaneously,
especially useful for studies of clusters of galaxies in the most distant
reaches, and earliest times, of the universe. LRIS was used in observing
distant supernovae by astronomers who received the Nobel Prize in Physics
in2011 for research determining that the universe was speeding up in its
expansion.
About W.M. Keck Observatory
The W. M. Keck Observatory telescopes are the most scientifically
productive on Earth. The two, 10-meter optical/infrared telescopes atop
Maunakea on the Island of Hawaii feature a suite of advanced instruments
including imagers, multi-object spectrographs, high-resolution spectrographs,
integral-field spectrometers, and world-leading laser guide star adaptive
optics systems. The data presented herein were obtained at the W. M. Keck
Observatory, which is operated as a scientific partnership among the California
Institute of Technology, the University of California, and the National
Aeronautics and Space Administration. The Observatory was made possible by the
generous financial support of the W. M. Keck Foundation. The authors recognize
and acknowledge the very significant cultural role that the summit of Maunakea
has always had within the Native Hawaiian community. We are most fortunate
to have the opportunity to conduct observations from this mountain.
