Helium Stars: A Stellar Relationship Analysis
Discover the intriguing lives of helium stars and their binary companions.
Sean Richards, Jan Eldridge, Sohan Ghodla, Max Briel
― 6 min read
Table of Contents
- What Are Helium Stars?
- Binary Stars: The Drama of Stellar Relationships
- Mass Transfer: When Stars Share Their Stuff
- The Importance of Studying Helium Stars
- The Complicated Lives of Binary Stars
- Mass Discrepancies: When Stars Misbehave
- The Role of Mass Transfer in Stellar Evolution
- The Mechanics of Mass Transfer
- Thermohaline Mixing: The Cosmic Stirring Spoon
- Tidal Forces: The Pull of Love (or Gravity)
- The Accretor's New Look
- The Impact of Helium-Rich Mass Transfer
- Future Evolution of Accretors
- The Yellow Supergiant Phase: A Time of Glory
- Implications for Supernovae Progenitors
- Conclusion: The Cosmic Love Story Continues
- Original Source
- Reference Links
Starry night, massive stars, and a bit of cosmic gossip! Welcome to the world of Helium Stars and their mischievous companions. You see, some stars are not alone; they like to hang out in pairs called binaries. They pass gas and, in some cases, steal helium from each other. This article is all about those helium stars and the fun (or troublesome) times they have in their stellar relationships.
What Are Helium Stars?
Helium stars are like the middle children of the stellar family. They sit between the smaller subdwarf helium stars and the flashy Wolf-Rayet stars. These stars have been through some changes and have lost a few layers of their hydrogen envelopes thanks to their binary partners. They are intriguing because they tell us a lot about the universe and how stars live and die.
Binary Stars: The Drama of Stellar Relationships
In the world of stars, binaries are like those couples who can't seem to separate. They exchange mass, which can lead to some surprising outcomes. When one star becomes a donor, it gets a bit stripped, and the other star, the accretor, takes in that lost material like a cosmic vacuum cleaner. This exchange can change their composition and affect their future.
Mass Transfer: When Stars Share Their Stuff
In a binary system, mass transfer is a big deal! One star gives some of its mass to the other, altering their orbits and how they evolve. It’s like sharing snacks, but instead of chips, they’re passing around hydrogen and helium. Sometimes, this process can lead to one star becoming a helium-rich beauty, while the other sits in envy.
The Importance of Studying Helium Stars
Why should we care about helium stars? Well, for starters, they can help us understand how stars evolve and interact. Plus, they can produce all sorts of interesting phenomena, like Supernovae and even gravitational waves. The more we study them, the more we learn about the universe and our place in it.
The Complicated Lives of Binary Stars
Binary stars live complicated lives. They constantly interact with their companions, leading to mass exchange and evolution that can differ from single stars. Studying both stars in a binary system lets us appreciate the rich tapestry of their combined life stories.
Mass Discrepancies: When Stars Misbehave
Sometimes, there’s a bit of a mix-up with star masses. Observations show discrepancies between their spectroscopic masses (what we think they are) and their evolutionary masses (what they actually are). This is often attributed to the unique processes happening in binaries, including the mass transfer and interaction with their partners.
The Role of Mass Transfer in Stellar Evolution
Consider mass transfer the starry equivalent of a game of hot potato. One star gives some of its mass to another, and this can leave both stars quite changed. It’s like a cosmic makeover, resulting in helium-rich stars with unique properties that reflect their recent past in a binary dance.
The Mechanics of Mass Transfer
When one star becomes a mass donor, it starts shedding material. The accretor then has to manage this influx of helium-rich material. The efficiency of this process can vary, leading to differences in how both stars evolve and interact.
Thermohaline Mixing: The Cosmic Stirring Spoon
During mass transfer, stars can mix elements like a chef mixing a pot of soup. This process, known as thermohaline mixing, can occur when heavier elements sink while lighter ones rise. In a binary system, this mixing can lead to even more unique compositions and behaviors in the accretor star.
Tidal Forces: The Pull of Love (or Gravity)
Imagine the tidal forces in a binary system as a stellar version of tug-of-war. Each star pulls on the other, creating changes in their shapes and even their spins. The closer they are, the stronger the pull, leading to some rather interesting outcomes in their evolution.
The Accretor's New Look
Once a star has accumulated enough helium, it doesn’t just become a bigger version of itself. Its inner layers can change radically, leading to a very different character compared to what it would have been if it lived alone. The accretor might develop a fancy new composition, with a helium-rich core and a hydrogen-rich envelope. This new look can affect everything from its temperature to how bright it shines.
The Impact of Helium-Rich Mass Transfer
When the accretor receives helium-rich material, it can become hotter and more luminous than expected. This is significant, as it means these stars contribute more ionizing photons to their environment than we might have thought. They could be like the rock stars of the cosmos, shining brightly and attracting attention.
Future Evolution of Accretors
After all this mass transfer craziness, what happens to our accretor star? It can have a unique evolutionary path that makes it stand out. These stars might live shorter lives but shine brighter, similar to celebrities who burn bright and fast.
The Yellow Supergiant Phase: A Time of Glory
Some accretor stars reach a phase where they become yellow supergiants. This period can be surprisingly short, especially for those who have undergone helium-rich mass transfer. But during this time, they can wow observers, becoming stars that are as bright as they are beautiful.
Implications for Supernovae Progenitors
Now, let’s talk about the end of the line for these stars. Some may become supernovae, and the interaction they had with their binary partners plays a massive role in how they explode. The unique makeup of helium-rich accretors could affect the types of supernovae we observe, possibly even shedding light on types we haven't fully understood yet.
Conclusion: The Cosmic Love Story Continues
Helium stars and their binary partners have quite a tale to tell. Their interactions shape their futures, leading to unique outcomes in the materials they produce and the forms they take. By studying these stellar relationships, we not only uncover the secrets of their existence but also gain insights into the broader picture of the universe’s evolution. So, here’s to helium stars - may their stories shine on for centuries to come!
Title: The variable evolution of accretor stars in binary systems due to accretion of increasingly helium-rich material
Abstract: The recent discovery of examples of intermediate-mass helium stars have offered new insights into interacting binaries. These observations will allow significant improvements in our understanding of helium stars. However, in the creation of these stars their companions may accrete a significant amount of helium-rich stellar material. These creates stars with unusual composition profiles -- stars with helium-rich cores, hydrogen-rich lower envelopes and a helium-rich outer envelope. Thus the mean molecular weight reaches a minimum in the the middle of the star rather than continuously decreasing outwards in mass. To demonstrate this structure we present Cambridge STARS model calculations of an example interacting binary systems where the helium-rich material is transferred, and compare it to one where the composition of the accreted mass is fixed to the companion's surface composition. We show that the helium-rich material leads to the accretor being 0.2 dex hotter and 0.15 dex more luminous than models where the composition is not helium rich. We use a simple BPASS v2.2 population model to estimate that helium-rich mass transfer occurs in 23 per cent of massive binaries that undergo mass transfer. This suggests this is a common process. This binary process has implications for the discrepancy between spectroscopic and gravitational masses of stars, the production of ionizing photons and possibly the modelling of high redshift galaxies.
Authors: Sean Richards, Jan Eldridge, Sohan Ghodla, Max Briel
Last Update: 2024-11-05 00:00:00
Language: English
Source URL: https://arxiv.org/abs/2411.03000
Source PDF: https://arxiv.org/pdf/2411.03000
Licence: https://creativecommons.org/licenses/by/4.0/
Changes: This summary was created with assistance from AI and may have inaccuracies. For accurate information, please refer to the original source documents linked here.
Thank you to arxiv for use of its open access interoperability.