Exploring Distant Galaxies: Uncovering New Planets – Sciworthy

In the iconic Star Wars series, an alien hero battles villains wielding planet-destroying superweapons set “a long time ago in a galaxy far, far away.” But what do scientists truly understand about alien planets in galaxies far beyond our own? These fascinating worlds are classified as extragalactic exoplanets. Assuming the Milky Way is similar to other galaxies, many such exoplanets are expected to exist. However, due to their vast distances, current exoplanet observation techniques have yet to uncover them.

Recently, a team of astronomers analyzed a stream of over 700,000 stars that the Milky Way may have absorbed from the Sagittarius Dwarf Galaxy. Given the remoteness of these stars, the researchers sought to determine whether any contained large exoplanets in close orbit to Earth, particularly hot Jupiters, which are relatively easier to detect.

To narrow their search, the team established three key criteria. First, each star needed to be bright enough for observation by a transiting exoplanet probe, specifically TESS, to ensure high accuracy in data processing. Second, each star had to have at least a 50% probability of originating from the Sagittarius Dwarf Galaxy, based on its motion and position as measured by the Gaia mission. Lastly, the stars needed to have a radius of less than twice that of the Sun to facilitate the detection of planets around smaller stars. This process refined their shortlist to approximately 20,000 stars.

After selecting potential stars, the team utilized a software package to analyze publicly available TESS catalog data, specifically the Eleanor TESS-Gaia light curve or TGLC. With these tools, they plotted the brightness of each star over time, creating a light curveTo identify hot Jupiters, they focused on brightness dips occurring every 14 hours to 10 days, which corresponds to the typical orbital periods of these exoplanets. The radius of each candidate exoplanet was then derived from the fraction of starlight blocked. Candidates with dips corresponding to objects with radii at least twice that of Jupiter were excluded, as these are likely caused by orbiting companion stars.

Among the stars studied, the most promising candidate for hot Jupiter was labeled TIC 92223525. It was estimated that this star could host an exoplanet with a radius 1.76 times that of Jupiter and an orbital period of 7.2 days. However, further examination revealed that its light curve was likely contaminated by the neighboring star TIC 92223526. The periodic brightness dips observed were mimicking those of an exoplanet, leading to a false positive for TIC 92223525, which was challenging to identify in the initial analysis. Consequently, the research team ultimately ruled out this candidate, leaving no confirmed exoplanets detected.

After their search for hot Jupiters yielded no results, researchers inferred that if over 1% of these stars hosted hot Jupiters, it would be very unlikely to find none in a sample exceeding 15,000 stars. This places the occurrence rate of hot Jupiters at approximately 1%. If this estimate holds true, even the best exoplanet-hunting teams would need to evaluate at least 11,000 stars to discover a hot Jupiter outside our galaxy. Factoring in scientific uncertainties, future research teams might need to examine as many as 80,000 stars to find just one.

While this survey of the Sagittarius Dwarf yielded no conclusive results, the research team urges future astronomers to continue exploring the Sagittarius Dwarf and other stellar streams from diverse galaxies. Scientists have already identified more than 20 such streams within the Milky Way. Investigating these flows may lead to the discovery of the first extragalactic planets or reveal that other galaxies produce fewer hot Jupiters than our own. Let’s hope that none of them come across the first extragalactic Death Star!

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