NASA's SPHEREx Caught a Nova Building Dust — and Watched Its Shell Cool From 1,030 K to 480 K

AHMEDABAD, India — A NASA space telescope that was never designed to study exploding stars has just delivered one of the clearest pictures yet of how a nova builds dust from scratch. Mining archival survey data from the SPHEREx mission, astronomers have traced the newborn dust shell around Nova Velorum 2025 — formally V572 Velorum — as it cooled from about 1,030 kelvin to roughly 480 kelvin over the course of a year, while its dust mass grew tenfold. The findings, reported in The Astronomer's Telegram on 29 October 2026, show a survey telescope doing cutting-edge transient science entirely as a byproduct of its main job: scanning the whole sky, over and over, without anyone asking it to look at this particular star.

The result matters beyond a single explosion. Dust is the raw material of planets, and the grains forged in stellar explosions carry chemical fingerprints that survive for billions of years, turning up in meteorites on Earth. Watching a dust shell form, expand, and cool in real time — with spectra spanning wavelengths that ground-based telescopes cannot reach — gives astronomers a rare benchmark for how those grains are born.

Illustration: A classical nova eruption, with a glowing shell of gas and newly forming dust expanding into space.

What Happened

A team led by D.P.K. Banerjee of the Physical Research Laboratory in Ahmedabad, India, reported the findings in The Astronomer's Telegram (ATel #18127), published 29 October 2026. Using two epochs of SPHEREx spectra, the team confirmed that V572 Velorum formed circumstellar dust after its eruption and mapped how that dust shell evolved thermally over more than a year.

The first SPHEREx dataset, covering wavelengths from 0.75 to 2.36 micrometres, was accumulated roughly 178 to 225 days after the eruption's reference epoch — around December 2025 through January 2026. Fitting a single blackbody curve to the infrared spectral energy distribution gave a dust temperature of about 1,030 kelvin. Assuming carbonaceous grains — a standard assumption for this class of nova — the inferred dust mass at that epoch was on the order of 10⁻⁹ solar masses: tiny, but measurable from space.

The second dataset, spanning 0.75 to 5.0 micrometres, was gathered roughly 334 to 393 days after the eruption — around June through August 2026. By then the shell had expanded substantially, and the same fitting procedure returned a temperature of about 480 kelvin, less than half the earlier value, with an inferred dust mass of about 10⁻⁸ solar masses — a tenfold increase. The pattern matches established models of nova dust evolution: as the shell expands and cools, conditions stay favorable for continued grain nucleation and growth over months.

Both spectra showed prominent emission features from hydrogen, helium, and oxygen — standard elements in nova spectra. The team also noted a possible detection of coronal emission lines, but cautioned that SPHEREx's low spectral resolution cannot identify individual emission species with confidence, and called for higher-resolution follow-up spectroscopy to confirm whether the lines are real.

Illustration: The SPHEREx space telescope sweeping the sky during its all-sky survey.

Background

V572 Velorum is no ordinary nova. It was discovered on 25 June 2025 by Australian observers John Seach and, independently, Andrew Pearce, when it erupted at visual magnitude 5.7. Within two days it had brightened to magnitude 4.8 — bright enough to see with the naked eye from the Southern Hemisphere — and a spectrum taken on 30 June 2025 confirmed it as an iron-type, or Fe II, classical nova, a category with a well-documented tendency to form dust.

Its pre-eruption record told a stranger story. Analysis of archival OGLE survey photometry revealed that the progenitor system had undergone multiple smaller outbursts between 2017 and 2024, identifying it as a dwarf nova of the SU Ursae Majoris subtype — a compact binary in which a white dwarf pulls material from a low-mass companion through periodic instabilities in its accretion disk. Classical novae arising from such progenitors are extremely rare; according to the research team, previously known cases are limited to V1213 Centauri and V392 Persei, making V572 Velorum only the third confirmed instance. Its orbital period was measured at 2.96 hours, and the Fermi-LAT gamma-ray telescope detected emission from the event in June 2025.

The nova's dust formation announced itself dramatically. About 25 days after discovery, monitoring by the American Association of Variable Star Observers recorded a deep optical "dust dip": the nova plunged from roughly magnitude 5.5 to around magnitude 12 before recovering. Such dips are the signature of dust condensing in nova ejecta — freshly formed grains absorb optical and ultraviolet light from the hot central source and re-radiate it at infrared wavelengths, dimming the visible brightness while brightening the infrared glow. The mechanism requires the ejecta to cool below approximately 1,500 kelvin, at which point grain nucleation becomes chemically favorable.

SPHEREx had, in fact, seen the eruption before anyone else. Images taken on 20 June 2025 — five days before the optical discovery — clearly showed V572 Velorum in outburst, captured automatically during standard survey operations. Banerjee and colleagues reported that precovery in January 2026, establishing 20 June 2025 as the accepted reference epoch for the eruption's timeline.

SPHEREx itself — the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer — launched from Vandenberg Space Force Base aboard a SpaceX Falcon 9 on 11 March 2025 and began science operations in May 2025. It is a joint project of NASA's Jet Propulsion Laboratory and the California Institute of Technology. Its primary goals are cosmological: mapping hundreds of millions of galaxies, probing the epoch of reionization, and characterizing water ice and other biogenic molecules in interstellar space. Nova dust was never on its agenda.

Illustration: A nova dust shell cooling as it expands, glowing hottest near the star and redder at its outer edge.

Why It Matters

The V572 Velorum result is one of the first demonstrations that SPHEREx's archival data can characterize nova dust evolution in near-real time — and it exposes a structural advantage that targeted telescopes cannot replicate. SPHEREx sweeps the full sky continuously with a heliosynchronous survey cadence, accumulating spectrophotometric data on every source bright enough to register. No target-of-opportunity interrupt is required and no observing time is "spent" on the nova; the data simply accumulates in publicly archived products at NASA's Infrared Science Archive, where any team can later extract transients with forced photometry.

That coverage reaches wavelengths Earth's atmosphere blocks. Ground-based near-infrared observatories can access windows around 1.25, 1.65, 2.2, and 3.5 micrometres, but cannot observe continuously across 2.5–5.0 micrometres, where strong water-vapor and carbon-dioxide absorption bands intervene. For nova dust, the longer wavelengths are critical: as dust cools below about 600 kelvin, its blackbody peak shifts beyond 5 micrometres, but the rising long-wavelength tail that constrains the temperature fit falls squarely in the range SPHEREx covers and the ground cannot. By the second epoch, with dust at 480 kelvin, the space-based 3–5 micrometre coverage was not merely convenient — it was the only practical source of that data.

An independent team at Caltech, Columbia, and associated institutions confirmed the emerging utility in a 2026 preprint: applying forced photometry to SPHEREx transient detections, they identified two new candidate FU Orionis stellar outbursts, re-classified three classical novae, and recovered one nova that had gone entirely unnoticed in optical surveys. The V572 Velorum result and those findings are independent demonstrations of the same principle: a space-based all-sky spectrometer generates transient science as a byproduct of its primary survey mission.

There is also a cosmic-accounting angle. Classical novae occur across the Milky Way at an estimated rate of 25 to 75 per year, though only a fraction are optically detected because dust obscures the Galactic plane. In aggregate, novae are minor contributors to the Galaxy's dust budget — asymptotic giant branch stars and supernova remnants dominate — with novae's total cumulative contribution estimated at only a few solar masses over the Milky Way's history. But nova grains are isotopically distinctive, carrying non-solar ratios of carbon, nitrogen, oxygen, neon, and magnesium forged in the thermonuclear runaway. Those signatures are recoverable in presolar grains found in primitive meteorites, making nova dust a forensic record of past Galactic chemical enrichment.

What Happens Next

The immediate next step is confirmation of the possible coronal emission lines. SPHEREx's spectral resolution — roughly R~40 at short wavelengths and R~110 at long wavelengths — smears adjacent spectral lines into broad, unresolved features, so it cannot distinguish real coronal lines from blending artifacts. The authors call for ground-based medium-resolution spectroscopy, such as instruments operating at R~2,000 or higher, to settle the question. Coronal lines matter because they indicate plasma at millions of degrees in the innermost ejecta and carry information about shock physics and white-dwarf-mass evolution.

More broadly, the nova community now faces a new division of labor: SPHEREx identifies and characterizes dust shells passively, while targeted ground- and space-based facilities supply the spectral detail it cannot. As SPHEREx's 25-month prime mission progresses toward its projected haul of spectra across roughly 14 billion sky pixels — surveying the full sky about four times over — its archive will only grow richer for transient science it was never designed to do.

And V572 Velorum itself is probably not finished. Its progenitor — a white dwarf in a close binary with a 2.96-hour orbital period — is still accreting, and its companion continues to transfer material. The classical nova eruption expelled the hydrogen that had built up on the white dwarf's surface, but the system remains active, and astronomers will keep watching for what it does next.

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FAQ

What is Nova Velorum 2025 (V572 Velorum)?

It is a classical nova — a thermonuclear eruption on the surface of a white dwarf in a close binary system — discovered in June 2025 in the constellation Vela. At its peak it reached magnitude 4.8, visible to the naked eye from the Southern Hemisphere.

What did SPHEREx measure?

Using archival spectra from two epochs, astronomers traced the nova's newborn dust shell as it cooled from about 1,030 kelvin (late 2025 to early 2026) to about 480 kelvin (mid-2026), while its inferred dust mass grew from roughly 10⁻⁹ to 10⁻⁸ solar masses.

Why is SPHEREx's role surprising?

SPHEREx is a cosmology survey telescope designed to map galaxies and probe the early universe. It captured the nova automatically during routine all-sky scans — including five days before its optical discovery — without any targeted observation request.

Why can't ground-based telescopes do this?

Earth's atmosphere blocks key infrared wavelengths, especially between 2.5 and 5.0 micrometres. As nova dust cools below about 600 kelvin, the data needed to measure its temperature falls in exactly the range only a space telescope like SPHEREx covers continuously.

Is the dust-shell finding confirmed?

The dust formation and cooling are established from two SPHEREx spectral epochs reported in The Astronomer's Telegram on 29 October 2026. A possible detection of coronal emission lines remains unconfirmed and needs higher-resolution follow-up spectroscopy.

Sources

Tech Times, "NASA SPHEREx Nova Find: Dust Shell Cooled From 1,030 K to 480 K in One Year," 30 October 2026; Banerjee et al., The Astronomer's Telegram #18127, "V572 Velorum: SPHEREx observations of dust formation and evolution," 29 October 2026; Banerjee et al., The Astronomer's Telegram #17601, SPHEREx precovery of V572 Velorum, January 2026.