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NICER / ISS Science Nugget
for May 8, 2025



NICER maps collision debris

NICER continues to push the boundaries of our understanding of the new astrophysical phenomenon known as quasi-periodic eruptions (QPEs). A peer-reviewed paper published this week in The Astrophysical Journal, led by MIT graduate student J. Chakraborty and accompanied by a NASA Science media release and video animation, describes measurements with NICER and ESA's XMM-Newton of "Ansky," an exceptional source of QPEs.

One of only 8 known QPE emitters, Ansky stands out for producing the most energetic and longest-lasting (about 1.5 days) eruptions, and for having the longest recurrence time between eruptions (approximately 4.5 days, in the data used by the Chakraborty et al. team). NICER's discovery of these eruptions was previously reported; the same dataset has now been analyzed spectroscopically, revealing absorption of X-rays at a photon energy that varies across the duration of each eruption. This study probes the physical conditions of the hot gas emitted when a stellar-mass body orbiting a supermassive black hole punches through the latter's accretion disk, in a so-called extreme mass-ratio inspiral (EMRI) scenario that is relevant to the science objectives of future gravitational-wave observatories. Modeling of an expanding, cooling "bubble" of debris expelled in each collision suggests that approximately 15 Jupiters worth of mass are released and speeds up to 15% the speed of light are reached. These represent the first insights into the content and energetics of the disk around the black hole at the center of Ansky's host galaxy, which in 2019 was seen to "awaken" in accreting matter from its environment, apparently leading to the formation of a disk and the interactions with a preexisting orbiting star that now reveal the entire system through X-ray eruptions from recurring collisions.

Followup observations of Ansky with NICER in early 2025 (enabled in part by the EVA repair of the light-leak experienced by the payload two years earlier) have been analyzed and submitted for publication, a paper that is currently in review.


NICER measurements (black points and inverted triangles) of the luminosity, in low-energy X-rays, of a subset of eruptions from Ansky in mid-2024. Colored vertical bands represent time ranges during which spectroscopic analysis yields the temperature of the gas glowing thermally in X-rays (101 eV represents approximately 1.2 million Kelvin). (Credit: Chakraborty et al. 2025) The full set of NICER-detected eruptions of Ansky in 2024 (dashed curves) overplotted with the energies (red points with error bars) at which X-rays are absorbed in a relatively narrow band; the rise and fall of these line energies traces the radius and speed of the debris bubble in each collision of an orbiting body with an accretion disk around a massive black hole. (Credit: Chakraborty et al. 2025)

Left: NICER measurements (black points and inverted triangles) of the luminosity, in low-energy X-rays, of a subset of eruptions from Ansky in mid-2024. Colored vertical bands represent time ranges during which spectroscopic analysis yields the temperature of the gas glowing thermally in X-rays (101 eV represents approximately 1.2 million Kelvin). (Credit: Chakraborty et al. 2025) Right: The full set of NICER-detected eruptions of Ansky in 2024 (dashed curves) overplotted with the energies (red points with error bars) at which X-rays are absorbed in a relatively narrow band; the rise and fall of these line energies traces the radius and speed of the debris bubble in each collision of an orbiting body with an accretion disk around a massive black hole. (Credit: Chakraborty et al. 2025)



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