We can measure the expansion of the universe with velocities and distances of extragalactic objects. But measuring distances is tough! The authors of this paper have developed a new technique for measure the distances of AGN using the “echo” of light from heated dust.
There’s a strange sickle-shaped object in the Carina Nebula. The authors of this paper used observations at several different wavelengths to investigate the nature of this intriguing nebula, leading to some interesting discoveries and even more questions.
Any photon with a wavelength shorter than 912 angstroms (the Lyman limit) will ionize neutral hydrogen by raising the atom’s electron from the ground state to an unbound state at infinity. From measurements of quasar absorption spectra, we know that the reionization of the intergalactic medium from its previously neutral state (at redshifts greater than 7) to the highly ionized state we observe today was complete by redshift of ~7. However, we still do not know which sources were responsible for producing the ionizing photons.
Everyone knows the Hubble Space Telescope — we saw its pictures growing up, and we use it now to probe everything from dark energy to planets’ genesis. But did you know in 2004 it came perilously close to extinction (and not the optical kind!)? The documentary “Saving Hubble,” which we profile here, tells the story of the battle for the great instrument’s survival.