As a result of its evolution, Sakurai’s Object also significantly increased in luminosity between 2006 and 2023. In this video, Sakurai’s Object is marked by the green circle.
Scientific Frontline: Extended "At a Glance" Summary: Sakurai's Object and "Born-Again" Stars
The Core Concept: A "born-again" star is a dead star, typically on its way to becoming a white dwarf, that temporarily re-ignites due to a rare late thermal pulse and resumes active evolution.
Key Distinction/Mechanism: Unlike typical stellar evolution that spans millions of years, this phenomenon is caused by the sudden re-ignition of a deep helium layer, causing the star to rapidly expand, cool, eject material, and transition into a Wolf-Rayet state within mere decades.
Origin/History: Sakurai's Object (along with V605 Aquilae) is one of only two directly observed stars undergoing this rebirth; it burst back to life in 1996 and has increased its temperature sixfold over the past thirty years.
Major Frameworks/Components:
- Very late thermal pulse (the sudden re-ignition of helium).
- White dwarf transition (the dense core phase interrupted by the pulse).
- Wolf-Rayet star characteristics (powerful stellar winds and distinctive carbon and helium signatures).
Branch of Science: Astronomy, Astrophysics, Stellar Evolution.
Future Application: Real-time observations provide critical empirical data to test, refine, and improve theoretical computer models simulating the shortest, final phases of a dying star's life cycle.
Why It Matters: This event offers a singular, rapid timeline allowing astronomers to witness and measure stellar evolutionary changes on a human timescale, rather than piecing together disparate data across millennia.
A team of astronomers led by the Royal Observatory of Belgium has found that a star called Sakurai’s Object has become six times hotter in the past 30 years, marking one of the fastest increases ever observed. Sakurai’s Object is a dead star that reignited in the 1990s as a "born-again" star. Thirty years ago, it was similar in temperature to our sun. It has now entered a new stage of stellar evolution, representing a Wolf-Rayet star. New observations show the star is reheating more gradually than some of the most recent theories predicted, providing an important test of theories describing the final stages of a star’s life. The rapidly changing star offers astronomers a rare opportunity to watch stellar evolution unfold in real time.
Using the European Southern Observatory’s Very Large Telescope (VLT) in Chile, researchers led by Peter van Hoof and Griet Van de Steene from the Royal Observatory of Belgium studied Sakurai’s Object, a rare "born-again" star that unexpectedly burst back to life in 1996 after reaching the final stages of its evolution.
Their findings, published today in the Monthly Notices of the Royal Astronomical Society, show that the star has entered a new phase of its evolution, developing the powerful stellar wind characteristic of Wolf-Rayet stars.
The research provides new insight into the final stages of stellar evolution and helps astronomers test theories that would otherwise take thousands or millions of years to verify.
Dr. Peter van Hoof of the observatory said, “For most stars, it is impossible to see them evolve on a human timescale. To understand their evolution, our only choice is to observe many different stars and piece together which of those are in different stages of the same path. Sakurai’s Object offers something far rarer. It is one of the very few stars known to have changed dramatically within just a few decades, giving us the opportunity to watch stellar evolution unfold in real time. With our observations, we can test theories of how stars evolve and gain new insights into one of the shortest and least understood phases in the life of a dying star.”
The scientists believe the star was similar to our sun but had already ended nuclear burning and begun its journey toward becoming a white dwarf—the hot, dense core left behind after an ordinary star dies. It underwent a rare event known as a “very late thermal pulse,” when a layer of helium deep inside the dead star suddenly reignites.
The event caused the star to rapidly expand, cool, and eject large amounts of material into space, temporarily returning it to an earlier stage of its life and leading astronomers to describe it as a “born-again” star.
Only two stars have ever been directly observed undergoing this type of dramatic rebirth: Sakurai’s Object and V605 Aquilae.
Following its outburst, Sakurai’s Object became hidden behind thick clouds of gas and dust released during the eruption, making it difficult to study directly.
To investigate its current state, the team analyzed light collected by the Very Large Telescope and compared it with sophisticated computer models that simulate the atmospheres and powerful winds of Wolf-Rayet stars.
The observations revealed distinctive signatures of carbon and helium, allowing the researchers to determine its temperature, chemical composition, and the characteristics of its stellar wind.
Their analysis suggests the star’s surface temperature is currently between 27,000 and 36,000 K, showing that it is reheating following its dramatic eruption nearly three decades ago.
Dr. Griet Van de Steene of the observatory added, “Sakurai’s Object evolved much more quickly than preexisting models for stellar evolution predicted. This led to a new generation of models that we now need to test. Our measurements show that the star is reheating more gradually than some of these new models predicted. That gives us an important way of testing which theories best describe what happens when a dying star briefly springs back to life. As we continue to monitor the star over the coming years, we expect to learn much more about this remarkable phase of stellar evolution.”
The findings also suggest that Sakurai’s Object is at an earlier stage of its evolution than V605 Aquilae, which experienced a similar event around 80 years ago.
The team will continue observing Sakurai’s Object as it continues reheating and resumes its journey toward becoming a white dwarf, learning more about one of the most rapid and unusual phases of stellar evolution ever observed.
Published in journal: Monthly Notices of the Royal Astronomical Society
Title: The emergence of a [WC] star in Sakurai’s object
Authors: W Marcolino, P A M van Hoof, V C Maria, H Todt, G C Van de Steene, J A Toalá, S Kimeswenger, M Hajduk, J -C Bouret, D Tafoya, D Barría, and A A Zijlstra
Source/Credit: Royal Observatory of Belgium
Edited by: Scientific Frontline
Reference Number: astr091626_01
