Detecting Remnants of White Dwarf Mergers

When two White Dwarfs collide, they often don't explode immediately. This paper looks into how we might spot the remaining pieces of these explosions, especially when two carbon-oxygen white dwarfs merge. For a time after the merger, these Remnants behave a lot like certain stars known as AGB stars, which eventually become massive white dwarfs. We find that it's easier to spot these remnants in big galaxies with lots of stars but not much star-making activity. However, spotting them is tough because they can look like other types of stars. One idea we have is to look for strange Nebulae around these remnants that give off light in unique ways.

#What Happens When White Dwarfs Merge

Merging white dwarfs can produce various results based on their combined size, the proportions of their masses, and their chemical makeup. Some of these Mergers cause explosions called Type Ia Supernovae, but many do not. Instead, they leave behind a remnant that can persist for a long time. If the mass of the merged remnant stays above a certain limit, it can eventually form a neutron star. If it's smaller, it may change into a cooling white dwarf or other types of stars.

In this discussion, we focus on mergers involving two carbon-oxygen white dwarfs or one carbon-oxygen and one oxygen-neon-magnesium white dwarf, as these will not create the other types of stars we mentioned earlier.

#The Timeline of a Merging Remnant

After a merger, the remnant takes time to evolve. This period can last for thousands of years, during which the remnant goes from being a giant star to a hot, young white dwarf. This evolution is similar to how regular stars change as they age. We compare the changes in these remnants to those seen in other types of stars and find significant overlaps in their brightness and temperature.

#Finding Merging Remnants

Identifying the remnants left behind by white dwarf mergers can be tricky. Although they might be bright, they often resemble other stars that are in different stages of their life. This similarity complicates identifying them based solely on brightness or temperature. In galaxies with less star formation, like the Milky Way or M31, it becomes a little easier to find these remnants among other stars, especially with different observational techniques.

#Techniques for Detection

To find these remnants, we considered two main techniques. The first involves trying to spot them based on how bright they are. We found this approach to be quite challenging. The second method seems more promising: we can look for the unique nebulae around these remnants. These nebulae are similar to those found around certain other types of stars and could give us clues about the presence of a white dwarf remnant.

#Estimating the Number of Merging Remnants

We can estimate how many remnants we might find in a galaxy by considering the rate at which these mergers happen and how long the remnants last. We assume that in a big galaxy like M87, there could be around a hundred of these remnants. This estimation helps us understand where to focus our search efforts for these intriguing objects.

#Why Finding Remnants is Hard

Despite the potential for finding these remnants, they can often be mistaken for other types of stars. In the Milky Way, we might be able to tell them apart based on where they are or by using special techniques, but in other galaxies, it's more challenging. To reduce confusion, we should focus on galaxies that are massive and not forming many new stars. These galaxies are more likely to have detectable white dwarf merger remnants.

#The Methods We'll Use to Spot Remnants

In this article, we will outline how we will attempt to detect these remnants. We will start by explaining our methods for creating a model of the stellar population in a galaxy that includes both normal and merged stars. We will also look into how the nebulae around these remnants behave and how we can compare them with planetary nebulae.

#The Challenge of Photometric Detection

While we have methods to identify these remnants, we also face many observational challenges. One big problem is that the remnants can get mixed up with classical novae and other similar stars. This overlap complicates the identification process. We will need to find ways to discern the differences between these similar-looking objects.

#Spectroscopic Signatures and Their Importance

Another section focuses on the unique light signatures that come from the nebulae around these remnants. These signatures are crucial for pinpointing white dwarf merger remnants. By understanding the light they emit, we can distinguish them from other objects in the universe.

#Synthesizing Color-Magnitude Diagrams

To help in our search for these remnants, we create color-magnitude diagrams (CMDs) simulating how our galaxy's star population looks. These diagrams allow us to compare the expected light from white dwarf merger remnants with other stars, helping us identify where to look.

#Results from Our Simulations

The diagrams we create show how merger remnants fit into the broader picture of stellar evolution. We find that they can stand out, especially in certain light wavelengths. However, we also note that many other stars can complicate this view, so we will need more advanced techniques to isolate the remnants.

#Looking at Nebulas and Their Spectra

Next, we will delve into the appearance of the nebulae surrounding the white dwarf remnants. We will use models to explore how these nebulae interact with light and what emissions they produce. This information is vital for understanding how to detect them.

#How Dust Affects Our Observations

Dust in the nebulae can significantly influence how we see these remnants. We'll discuss how dust affects the light emitted and how this complicates our ability to observe the remnants in detail.

#Observing in External Galaxies

Finding these nebulae in external galaxies presents its own set of challenges. The background light from all the stars can make it difficult to spot the faint emissions from the remnants. We will discuss how we can overcome these challenges and what strategies might work best.

#The Case of IRAS 00500+6713

One interesting object we can discuss is IRAS 00500+6713, which might be a white dwarf merger remnant. We'll look at its characteristics and how they align with our expectations for such remnants. This example will help illustrate the points we've made throughout the paper.

#Summary and Future Work

In conclusion, many white dwarf mergers likely don't lead to immediate explosions. Instead, they can leave behind remnants that we may be able to find. Searching for these remnants in galaxies with low star formation rates could be fruitful, especially for those in the Milky Way and similar systems.

As we continue our work, we hope to refine our methods and predictions for detecting these remnants. There are many uncertainties that we still need to address, such as the nature of the dust around the remnants and how best to model their properties. Future observations will help clarify these aspects, and we will continue to improve our understanding of white dwarf mergers and their remnants.