Which NASA space telescope helped reveal the Milky Way's central bar in infrared surveys?

The NASA space telescope that helped reveal the Milky Way’s central bar in infrared surveys was the Spitzer Space Telescope.

Spitzer was designed for infrared astronomy, a crucial advantage for studying the Galactic plane. Visible light from distant stars is heavily absorbed by clouds of dust, but infrared wavelengths pass through much of that obscuring material. Spitzer’s GLIMPSE surveys therefore mapped millions of stars across the inner Milky Way and exposed large-scale structure that optical surveys could not trace reliably.

In 2005, analyses of Spitzer observations provided strong evidence that the Galaxy has a substantial stellar bar crossing its central region. The bar is made mainly of older stars and connects to the inner parts of the spiral structure; it is distinct from Sagittarius A*, the supermassive black hole at the exact center.

Spitzer did not discover the Milky Way’s central black hole, and it was not an X-ray observatory like Chandra. Hubble also observes some infrared light, but the wide-area, dust-penetrating surveys that mapped the bar were a signature achievement of Spitzer’s infrared instruments. Spitzer launched in 2003 and was retired in 2020.