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Astronomers have made a groundbreaking discovery, identifying a “missing link” in the stellar evolution process: a “teenage vampire” white dwarf. This celestial object helps bridge the gap between the demise of sun-like stars and the formation of white dwarf remnants. This unique find provides valuable insights into the life cycle of stars and the fascinating phenomena that occur at the end of their existence.
Contrary to its moniker, this vampire doesn’t thirst for blood. The white dwarf, known as Gaia22ayj, resides around 8,150 light-years away from Earth and is actively consuming stellar plasma from a neighboring star.
The discovery team utilized the Zwicky Transient Facility (ZTF) at the Palomar Observatory in California to observe this peculiar white dwarf. Their research involved scanning the Northern Hemisphere’s night sky, searching for “transients,” which are astronomical entities undergoing quick alterations.
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Gaia22ayj initially gained the attention of astronomers due to its rapidly fluctuating signal. This characteristic led to its initial classification as a detached double white dwarf binary, consisting of two white dwarf stars revolving around each other.
However, this preliminary assessment didn’t align with subsequent observations of Gaia22ayj. These later observations revealed it to be one of the most remarkably pulsating objects ever observed, with its brightness surging by 700% in just two minutes.
This unusual behavior indicated that Gaia22ayj is, in fact, a white dwarf feeding off a companion star, placing this binary system in an uncommon and transient stage of its existence.
Understanding Stellar Demise
Stars meet their end once they exhaust the necessary fuel for nuclear fusion. The nature of their demise and subsequent “afterlife” is contingent on their mass.
Stars exceeding eight times the mass of our sun end their lives in powerful supernova explosions. They then transition into either ultra-dense neutron stars or black holes. Stars closer in mass to our sun undergo a more gradual transformation into white dwarfs.
Our sun will follow this latter path in roughly six billion years. It will shed much of its mass during an expanded red giant phase before ultimately fading away as a smoldering stellar remnant.
The Role of Binary Companions
Roughly half of all stars with masses comparable to the sun exist with a binary companion star. If these companion stars come too close, white dwarfs can experience a resurgence by extracting stellar material from them. This vampiric mass transfer is precisely what appears to be happening between Gaia22ayj’s white dwarf and its companion star.
Initially, Gaia22ayj confused researchers. The way its light intensity varied over time – its light curve – didn’t conform to expectations for a detached double white dwarf binary.
This prompted Tony Rodriguez, a graduate student at Caltech’s ZTF Stellar Group, to investigate the unusual light curve. By compiling additional data, Rodriguez and his team concluded that Gaia22ayj is likely a white dwarf accompanied by a “normal,” low-mass star, not a second white dwarf. They also determined that Gaia22ayj is intensely magnetic, with its white dwarf component spinning rapidly.
This discovery drew parallels to a white dwarf pulsar, an extremely magnetic dead star that emits electromagnetic radiation as it rotates, resembling a cosmic lighthouse. However, the vampiric feeding process observed in Gaia22ayj is not usually associated with white dwarf pulsars.
The Missing Link in White Dwarf Evolution
Ultimately, the team reasoned that Gaia22ayj represents a crucial missing link in the life cycle of white dwarf pulsars, signifying a rare and short-lived early phase of these objects.
“We had already observed two nascent systems, white dwarf stars in a binary system where rapid spin generates a strong magnetic field. Additionally, we had seen numerous mature star systems with slowly rotating white dwarf stars,” Rodriguez explained in a statement.
“However, this marks the first star we’ve detected in the midst of its ‘teenage’ phase. It has already established a robust magnetic field and is just initiating the process of funneling matter from its companion star onto itself,” he continued. “Never before have we observed a system simultaneously spinning so rapidly while also dramatically decelerating, all while gaining mass from its companion.”
This discovery gains further significance when considering that this phase lasts only about 40 million years. While this duration seems considerable, it is relatively brief compared to the lifespan of stars like our sun, which live for around 10 billion years before transforming into white dwarfs. Hence, this “teenage phase” accounts for just 0.4% of a star’s lifetime. If the star were an average human, this teenage phase would equate to approximately 107 days.
Barely enough time for a significant change.
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“The data acquired at the W. M. Keck Observatory offered compelling proof that this system possesses a strong magnetic field and is directing matter onto the white dwarf,” Rodriguez stated. “Further data from the unique instruments available at Palomar Observatory revealed that this system is, remarkably, decelerating.”
The research team’s findings were published in February in the journal Publications of the Astronomical Society of the Pacific.