🔭 astrophysics

Repeating flares, X-ray outbursts and delayed infrared emission: A comprehensive compilation of optical tidal disruption events

This paper introduces TDECat, a comprehensive catalogue of 134 confirmed tidal disruption events discovered by the end of 2024, and presents statistical analyses of their multi-wavelength properties, spectral classifications, and temporal behaviors to facilitate large-scale population studies for future astronomical surveys.

Original authors: D. A. Langis, I. Liodakis, K. I. I. Koljonen, A. Paggi, N. Globus, L. Wyrzykowski, P. J. Mikołajczyk, K. Kotysz, P. Zieliński, N. Ihanec, J. Ding, D. Morshed, Z. Torres

Published 2026-01-22

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CC BY 4.0

Original authors: D. A. Langis, I. Liodakis, K. I. I. Koljonen, A. Paggi, N. Globus, L. Wyrzykowski, P. J. Mikołajczyk, K. Kotysz, P. Zieliński, N. Ihanec, J. Ding, D. Morshed, Z. Torres

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe as a giant, dark ocean, and at the bottom of this ocean sit massive, invisible whirlpools called Supermassive Black Holes. Usually, these whirlpools are dormant, sleeping quietly. But occasionally, a star (like our Sun) wanders too close. The whirlpool's gravity is so strong that it stretches the star like taffy until it rips apart. This violent event is called a Tidal Disruption Event (TDE).

For a long time, astronomers have been trying to study these events to understand the sleeping black holes, but they've been like detectives trying to solve a mystery with only a handful of clues. There just haven't been enough observed events to see the big picture.

This paper introduces TDECat, a massive new "phone book" or catalogue that collects every confirmed TDE discovered up to the end of 2024. Think of it as the first time someone has gathered all the scattered puzzle pieces into one complete box. Here is what the authors found by looking at this new collection:

1. The "Recipe" for a Black Hole Meal

The authors looked at 134 of these events. They measured how long the "flare" (the bright flash of light) took to rise, how long it took to fade, and how long the whole show lasted.

The Analogy: Imagine baking a cake. You want to know how long it takes to rise in the oven and how long it takes to cool down.
The Finding: They found that the timing of these cosmic "cakes" follows a very predictable pattern, like a bell curve. Most events have a "standard" rise and fall time, just like most cakes take about the same amount of time to bake. They also discovered that the rise time and the decay time are linked: if a flare rises quickly, it tends to fade quickly too.

2. What Was the Star Made Of?

When a star is ripped apart, it leaves behind a "soup" of gas that glows. By looking at the colors (spectra) of this light, astronomers can tell what kind of star was eaten.

The Analogy: It's like looking at the smoke from a campfire to guess what wood was burning. Is it pine (hydrogen) or oak (helium)?
The Finding: Most of the stars eaten were normal, main-sequence stars (like our Sun), which are made of both hydrogen and helium. This is the most common type of star in the center of galaxies, so it makes sense that they are the most common "snack" for black holes. A few were made mostly of helium, and a few were so messy or obscured that they looked "featureless."

3. The "Repeat Offenders"

Some black holes don't just eat one star and stop. Sometimes, they take a bite, spit the star out, and then come back for a second bite later.

The Analogy: Imagine a shark that takes a bite out of a swimmer, lets them swim away, and then attacks them again a year later.
The Finding: The authors found 11 such "repeat offenders." They identified three new cases (AT 2024pvu, AT 2022exr, and AT 2021uvz) that hadn't been noticed before. Interestingly, the second "bite" (the second flare) often looks almost identical to the first one, suggesting the same star is being torn apart in pieces over time. One of these events had a gap of nearly 18 years between flares!

4. The Multi-Color Connection

TDEs don't just glow in visible light; they also emit X-rays (high energy) and Infrared light (heat).

The Analogy: If you see a fire, you expect to see smoke (infrared) and feel the heat (X-rays). You wouldn't expect a fire to glow red without any heat.
The Finding: The authors found a strong link between these different types of light. If a TDE glows brightly in infrared, it is very likely to also glow in X-rays. They calculated that this connection is not just a coincidence; it's a real physical relationship. This suggests that the same process is creating both the heat and the high-energy radiation.

Why Does This Matter?

The paper concludes that by having this big, organized list of 134 events, astronomers can finally stop guessing and start doing real statistics. It's like moving from looking at a single drop of rain to studying a whole storm.

This catalogue is a tool for the future. With new telescopes coming online that will spot thousands of these events, having a solid reference guide like TDECat will help scientists navigate the flood of new data and understand the mysterious behavior of the universe's most voracious monsters.

Problem Statement
Tidal disruption events (TDEs) are proposed as valuable laboratories for studying dormant supermassive black holes (SMBHs). However, progress in this field has been significantly hampered by the limited number of observed events. While approximately 10–20 new optical TDEs are detected annually, no comprehensive, unified catalogue existed to facilitate robust statistical analyses. The lack of a consolidated dataset with multi-wavelength photometry and spectroscopy prevented large-scale population studies necessary to understand the diversity and physical mechanisms of these events.

Methodology
The authors constructed TDECat, a comprehensive catalogue of 134 confirmed TDEs discovered up to the end of 2024. The sample selection process involved:

Data Sources: Retrieving 105 sources from the Transient Name Server (TNS) and 29 sources from published literature (including studies by Hammerstein et al. 2023 and Yao et al. 2023).
Inclusion Criteria: The main catalogue includes events with at least one optical photometric survey detection and an available classification spectrum from the time of the flare. It also includes TDEs with featureless spectra and three widely accepted on-axis jetted TDEs. Sources lacking flare-time spectra were designated as "TDE candidates" in a separate supplementary table.
Data Compilation: The authors aggregated publicly available photometric data (X-ray, UV, optical, and infrared) from surveys including ZTF, ASAS-SN, ATLAS, Pan-STARRS, CRTS, Swift, Chandra, XMM-Newton, and NEOWISE. All magnitudes were converted to the AB system. Spectroscopic data were sourced from TNS, WISeREP, and specific literature tables.
Analysis Techniques:
- Light Curve Analysis: A Bayesian Blocks algorithm was applied to 103 flares to determine duration, rise time ( $t_{rise}$ ), decay time ( $t_{decay}$ ), and their ratio.
- Statistical Testing: Kolmogorov-Smirnov (KS) and Anderson-Darling (AD) tests were used to assess the distribution of timescales and redshifts. Orthogonal Distance Regression (ODR) was employed to analyze the correlation between rise and decay times.
- Spectral Classification: Events were categorized into four classes (TDE-H, TDE-H+He, TDE-He, TDE-featureless) based on established definitions.
- Sub-sample Analysis: The authors investigated specific sub-populations: repeating flares, infrared (IR) emitting events, and X-ray emitting events, testing whether their spectral classes were randomly distributed relative to the full sample.

Key Contributions

TDECat Catalogue: The primary contribution is the release of a unified dataset containing 134 confirmed TDEs (131 optical and 3 jetted) with multi-wavelength photometry and spectra, accessible via a GitHub repository and a Python application.
Identification of New Repeating Events: The study identified three new potentially repeating TDEs (AT 2024pvu, AT 2022exr, and AT 2021uvz) through archival observations, increasing the known population of repeating events.
Standardized Light Curve Metrics: The application of the Bayesian Blocks algorithm provided a consistent method for deriving rise and decay times for a large sample (103 flares), overcoming previous limitations of small sample sizes.

Results

Timescale Distributions: The distributions of flare duration, rise time, decay time, and the $t_{rise}/t_{decay}$ ratio were found to follow a log-normal distribution. A positive correlation was confirmed between rise and decay times ( $\log_{10}(t_{rise}) = 0.915 \log_{10}(t_{decay}) - 0.31$ ), contradicting earlier findings from smaller samples that suggested no correlation.
Spectral Classification: The majority of optical TDEs (60.3%) belong to the TDE-H+He class, followed by TDE-H (17.6%), TDE-He (12.2%), and TDE-featureless (9.9%). This distribution aligns with expectations for the disruption of main-sequence stars.
Repeating Flares: In the 11 identified repeating-flare TDEs, secondary flares generally exhibited shapes similar to the primary flares. The authors analyzed mechanisms such as partial TDEs (pTDE), stellar binary disruptions, and separate events, finding that pTDEs and binary disruptions are plausible explanations for most cases, while separate events are statistically unlikely for sources with short time separations.
Multi-wavelength Correlations:
- IR and X-ray: A strong potential correlation exists between IR and X-ray emission; 14 out of 18 IR-flaring TDEs had associated X-ray detections. Statistical testing rejected the null hypothesis of random association ( $P \approx 3.3 \times 10^{-4}$ ).
- Spectral Sub-samples: The spectral classes within sub-samples (repeating flares, IR-emitting, and X-ray-emitting) were found to be unlikely to be randomly distributed, suggesting a connection between spectral characteristics and multi-wavelength emission properties.
Redshift: The redshift distribution of the sample follows a log-normal distribution, likely influenced by observational selection effects and local galaxy density.

Significance
The paper claims that TDECat provides an essential tool for navigating the "data-rich era" of upcoming surveys like the Legacy Survey of Space and Time (LSST). By enabling large-scale population studies across wavelengths and spectral classes, the catalogue allows for robust statistical analyses that were previously impossible due to small sample sizes. The authors emphasize that the derived log-normal distributions of timescales and the identified correlations between spectral classes and multi-wavelength emission can be used to generate mock data for future statistical studies and machine learning applications, aiding in the interpretation of the tens of TDEs expected to be captured nightly by future surveys.

1. The "Recipe" for a Black Hole Meal

2. What Was the Star Made Of?

3. The "Repeat Offenders"

4. The Multi-Color Connection

Why Does This Matter?

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