KELT-9

Star

KELT-9 — a hot, blue-white A0/B9.5 star about 2.5 solar masses and over 10,000 K, ~667 light-years away in Cygnus. Its blistering ultraviolet output makes its close-in planet the hottest known — and is boiling that planet's atmosphere away.

Open in 3D viewSee KELT-9 in the live, interactive 3D map

Key facts

Mass

5.01 × 10³⁰ kg

2.52 M☉

Radius

1,643,243 km

2.36× wider than the Sun

Surface temperature

10,170 K (9897 °C)

Spectral type

B9.5/A0 (a hot blue-white star, ~2.5 solar masses)

Science

Physical

Mass: 5.01 × 10³⁰ kg · 2.52 M☉
Radius: 1,643,243 km · 2.36× wider than the Sun
Density: 270 kg/m³ · 0.27× water
Spectral type: B9.5/A0 (a hot blue-white star, ~2.5 solar masses)

Composition

By mass: A hot, luminous early-A / late-B star over 10,000 K — far hotter than the Sun. Its fierce ultraviolet output is what makes its close-in planet the hottest known and is evaporating that planet's atmosphere.

Temperature

Surface: 10,170 K (9897 °C)

Radiation & temperature

Luminosity: 2.06 × 10²⁸ W · 53.8 L☉
Surface temperature: 10,170 K (9897 °C)
Peak wavelength: 285 nm · ultraviolet (invisible to the eye)

Discovery & history

Name: A KELT-survey designation (also HD 195689).

A bright, hot star whose shallow transit in 2017 revealed the record-breaking planet.

Images

Where to find it — in Cygnus, the Swan (IAU constellation chart). To the eye it is a single point of light; no telescope has imaged its surface. — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image