In an exciting breakthrough for the field of astronomy, a team of researchers has managed to track down the source of a mysterious type of radio pulse emanating from deep space, and the discovery is far from what astronomers had anticipated. For the past three years, astronomers have been grappling with the enigmatic phenomenon of long period transients – objects that emit bright radio signals at intervals ranging from a few minutes to several hours. These objects were puzzling, as they did not align with known sources like pulsars or white dwarfs, leaving the scientific community to wonder what exactly could be producing these peculiar emissions.
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However, new research published in Nature Astronomy today has provided a breakthrough, identifying the stars responsible for the long period transients – and in a twist, they are not the typical “cosmic lighthouses” that researchers had expected. These stars have been found to be white dwarfs, a finding that challenges our understanding of how these objects can emit such intense, periodic radio pulses.
What Are Cosmic Lighthouses?
Before diving into the specifics of this new discovery, it’s important to understand the conventional sources of radio pulses in space. One of the most well-known culprits is the pulsar – a type of neutron star. Neutron stars are the remnants of supernovae explosions of massive stars. When they collapse under immense gravity, they form dense and incredibly small remnants that spin rapidly. Pulsars emit beams of radio waves from their poles, and as the neutron star spins, these beams sweep across the universe, creating the characteristic pulses detected by radio telescopes on Earth. These pulsars are often referred to as “cosmic lighthouses” because their rotating beams of radio waves resemble a lighthouse beacon in their sweeping motion.
Pulsars emit signals at regular intervals, typically every second or less, depending on their rotation speed. However, long period transients behave very differently. These objects emit radio pulses that repeat much more slowly, with some sources emitting pulses every few minutes or even hours. According to theories surrounding neutron stars, pulsars with such long rotational periods should not exist – at least, not in the way we have observed these new sources.
A Cosmic Detective Hunt
In a new study, researchers used the international LOFAR radio telescope, located in Europe, to investigate the nature of these long period transients. The team discovered a previously unidentified object named ILTJ1101+5521, and upon careful analysis of the data, they found seven distinct radio pulses. These pulses arrived with an uncanny regularity – every 125.52978 ± 0.00002 minutes, or precisely every two hours.
This discovery confirmed that ILTJ1101+5521 is indeed a long period transient, and the next step was to pinpoint the source of these mysterious radio emissions. To do so, the researchers compared the location of the pulses to existing optical catalogues, which list the stars and galaxies that have been observed in visible light. When they cross-referenced their data, they found a faint red star situated precisely at the source of the radio pulses.
However, the characteristics of the radio pulses indicated that the red star alone could not be the source of the emissions.
A Hidden Companion Star
Many stars exist in binary systems, where two stars are gravitationally bound to one another and orbit a common center of mass. It is believed that about half of stars similar in size to our Sun are part of binary systems. The researchers decided to take a closer look at the red star’s spectral data to determine if a hidden companion could be influencing the radio signals.
By examining the star’s spectral “fingerprint,” which reveals the wavelengths of light the star emits, they observed a shifting of the wavelengths over time. This shifting, known as the Doppler effect, occurs when a star moves towards or away from the observer. In this case, the movement indicated that the red star was in motion, as it alternately approached and receded from Earth. This movement could only be explained if the red star was orbiting another stellar object.
The data revealed that the two stars in the system were orbiting each other every two hours, matching the exact timing of the radio pulses detected. This observation led the researchers to hypothesize that the mysterious radio signals were coming from a binary star system – and more specifically, from a white dwarf in orbit with a red star.
Unveiling the White Dwarf
White dwarfs are the remnants of lower-mass stars, like our Sun, that have exhausted their nuclear fuel. When these stars reach the end of their life cycle, they shed their outer layers, leaving behind a dense, Earth-sized core known as a white dwarf. These objects are much smaller than neutron stars but still incredibly dense.
Using photometric measurements taken over a broad range of wavelengths, the researchers found an excess of blue light in the data, which could not be attributed to the red star alone. This additional blue light suggested the presence of a white dwarf, as these objects emit blue light due to their high temperature. The combination of the shifting spectra and the blue excess led the team to conclude that the radio pulses were coming from the white dwarf, and the red star was its companion in a binary system.
A New Type of Radio Source
This discovery represents a significant shift in our understanding of long period transients. While pulsars and neutron stars have long been considered the primary sources of periodic radio pulses, this new finding suggests that white dwarfs, with the help of a companion star, can also produce similarly intense and regular radio emissions.
However, the researchers caution that not all long period transients are likely to be white dwarf binaries. Some transients show characteristics that are more closely aligned with pulsars, and others have shorter periods that would be inconsistent with the orbital periods observed in white dwarf binaries.
As the field of radio astronomy continues to explore the origins of these mysterious radio pulses, further observations will be necessary to fully understand the variety of long period transients and their diverse sources.
Looking Forward
The discovery of the long period transient ILTJ1101+5521 and its white dwarf binary companion opens a new chapter in the study of radio sources in space. It also highlights the importance of continuing to search for and study these enigmatic objects, as each new finding deepens our understanding of the cosmos. Though this breakthrough answers one important question, it raises many more, and the pursuit of these cosmic mysteries is far from over.
As astronomers push forward with their investigations, the search for additional long period transients will help refine our theories about the nature of these objects and their place in the vast universe.
