Kostas Migkas

Oort fellow at Leiden Observatory. Working on X-ray galaxy clusters and observational cosmology. Dad and husband.

[Kostas Migkas @KMigkas]

Galaxy clusters and cosmology are coming together in Leiden and our upcoming Lorentz Workshop! Contact us if interested in joining!

Cosmology at the Crossroads: Galaxy Clusters in the Era of Large Surveys
📅 8–12 Dec 2025

👉 https://t.co/1adQkZGwaq
#Cosmology #GalaxyClusters

[Chandra Observatory @chandraxray]

The Bullet Cluster is iconic, having provided the first direct proof of dark matter with NASA's Chandra, Hubble, and ground-based telescopes back in 2006. This spectacular new image combines Chandra & Webb Telescope data — helping us learn more about dark matter than ever before.

[Nereide @Nereide]

At a distance of about 2.5 Mly, the Andromeda galaxy (M31) is our closest cosmic neighbor, a perfect laboratory for exploring the Universe.

This spectacular new image, created by combining data from telescopes Chandra, XMM-Newton, GALEX, Spitzer, and others, gives us an unprecedented view of it.
Every of the five wavelengths used – X-ray, ultraviolet, optical, infrared and radio – reveals unique details, such as compact objects in the galaxy and the activity of M31*, the supermassive black hole at its center. This composite image, about 150,000 ly across, accompanied by a sonification (read the reference) that transforms the data into sounds, makes science accessible to all, celebrating the legacy of Vera Rubin, a pioneer in the discovery of dark matter.

In 1960, Rubin studied the motions of stars in Andromeda galaxy, providing some of the first evidences for the existence of dark matter (DM), an invisible substance influencing the gravity of galaxies. The new M31 image, released in her honor, is a tribute to her legacy, while data from Chandra deepen our gaze on the central supermassive black hole (SMBH).

A recent study (in The Astrophysical Journal, 2025) analyzed 15 years of Chandra observations (2009–2024), revealing that the SMBH, M31*, has remained in a state of high X-ray emission since 2006, with a luminosity of about 10³⁶ erg per second.

A key event was a flare in 2013, when the X-ray flux increased fivefold compared to the post-2006 average level. Thanks to the low activity of nearby sources, scientists were able to study the spectrum of this flare, finding similarities with the Milky Way's quiescent black hole, Sgr A*.

Unlike the more intense flares of Sgr A*, the flare of M31* appears to be an amplification of its normal emission processes, not a radical change. This makes M31* a unique case to compare the behavior of supermassive black holes.

Why is Andromeda so important?
As the closest spiral galaxy, it helps us understand our Milky Way. The 2013 flare is also an ideal candidate for future studies with instruments such as the Very Large Array radio telescope or the IceCube neutrino detector, which could reveal new details about the energetic processes in galactic nuclei. However, the paucity of observations between 2016 and 2021 highlights the need for continued monitoring with high-resolution telescopes such as Chandra or the future Advanced X-ray Imaging Satellite (AXIS).

This discovery combines the beauty of the universe with frontier science. Thanks to Vera Rubin and instruments like Chandra, Andromeda continues to tell us the secrets of the cosmos, bringing us closer to understanding the black holes and dark matter that shape galaxies.
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Image credit: X-ray: NASA/CXO/UMass/Z. Li & Q.D. Wang, ESA/XMM-Newton; Infrared: NASA/JPL-Caltech/WISE, Spitzer, NASA/JPL-Caltech/K. Gordon (U. Az), ESA/Herschel, ESA/Planck, NASA/IRAS, NASA/COBE; Radio: NSF/GBT/WSRT/IRAM/C. Clark (STScI); Ultraviolet: NASA/JPL-Caltech/GALEX; Optical: Andromeda, Unexpected © Marcel Drechsler, Xavier Strottner, Yann Sainty & J. Sahner, T. Kottary. Composite image processing: L. Frattare, K. Arcand, J.Major

Reference➡️https://t.co/BSPWSO1cwr

Research paper: 'Fifteen Years of M31* X-Ray Variability and Flares', Stephen DiKerby et al 2025 ApJ 981 50➡️https://t.co/7bmKddaovb

[ESA XMM-Newton @ESA_XMM]

“The models were right”: astronomers find ‘missing’ matter. Astronomers have discovered a huge filament of hot gas bridging four galaxy clusters. The thread could contain some of the Universe’s ‘missing’ matter, addressing a decades-long mystery.

https://t.co/CZKamiE1i7

[Dr Maggie Lieu @Space_Mog]

Huge congrats to my collaborators @KMigkas & @FlorianPacaud on their groundbreaking work on the universe's missing matter, a significant step in understanding the cosmos. So proud to work alongside such brilliant minds! 🚀 https://t.co/zN77OEPCKh

[ESA Science @esascience]

For decades, astronomers have been searching for the missing 30–40% of 'normal' visible matter that models tell us should exist in the Universe.

But it's not in stars, galaxies, planets or pet cats.

Finally, they've found it 👉 https://t.co/5O1ofV5gjU

[Kostas Migkas @KMigkas]

@OFA_astronomy @ESA_XMM @JAXA_en Ευχαριστώ πολύ, είναι άριστο!

[Kostas Migkas @KMigkas]

📢Paper and press releases day! We report the first-ever unambiguous detection of WHIM/missing baryons in a single cosmic filament using @ESA_XMM and @JAXA_en Suzaku data! It's the first time observations agree with LCDM simulations for the nature of WHIM https://t.co/ozeCaZLjXs

[Kostas Migkas @KMigkas]

Finally, @AandA_journal made us their featured image 🙂 https://t.co/6l8ciJ2yEF

[Kostas Migkas @KMigkas]

The cosmic filament is 7.2 Mpc long, exhibits ~20% excess emission compared to the background, has a temperature of ~1 keV, gas particle density of ~10^-5/cm^3, and a baryon overdensity of ~35, making it the first pristine single filament ever detected in Xrays!

[Kostas Migkas @KMigkas]

Delighted to share that I got yet another research grant from @UniLeidenNews and the Fonds Rijke-Hamaker fund! 🥳 This grant will support the analysis of new X-ray galaxy cluster data obtained by @ESA_XMM for further refining our understanding of cosmic expansion uniformity!

[Kostas Migkas @KMigkas]

🚀 Exciting news! Our proposal for the Lorentz Workshop, focusing on Cosmology with Galaxy Clusters is approved for 8–12 Dec 2025 🎉
@lorentzcenter @LeidenU
We'll bring together cluster enthusiasts and dive into the latest in cluster cosmology! https://t.co/2yp9H04lUy

[South Pole Telescope @SPTelescope]

The proposed FY26 budget will be devastating for NASA science with a nearly 50% cut: 11 NASA astrophysics missions face risk of cancellation https://t.co/mLdLP7A34D