Solar-mass stars form via disk-mediated accretion. Recent findings indicate that this process is probably episodic in the form of accretion bursts 1 , possibly caused by disk fragmentation 2-4 . Although it cannot be ruled out that high-mass young stellar objects arise from the coalescence of their low-mass brethren 5 , the latest results suggest that they more likely form via disks 6-9 . It follows that disk-mediated accretion bursts should occur 10,11 . Here we report on the discovery of the first disk-mediated accretion burst from a roughly twenty-solar-mass high-mass young stellar object 12 . Our near-infrared images show the brightening of the central source and its outflow cavities. Near-infrared spectroscopy reveals emission lines typical for accretion bursts in low-mass protostars, but orders of magnitude more luminous. Moreover, the released energy and the inferred mass-accretion rate are also orders of magnitude larger. Our results identify disk-accretion as the common mechanism of star formation across the entire stellar mass spectrum.S255IR NIRS 3 (aka S255IR-SMA1) is a well-studied ∼20 M (L bol ∼ 2.4×10 4 L ) high-mass young stellar object (HMYSO) 13,14 in the S255IR massive star-forming region 13 , located at a distance of ∼1.8 kpc 15 . It exhibits a disk-like rotating structure 13 , very likely an accretion disk, viewed nearly edge-on 16 (inclination angle ∼80 • ).A molecular outflow has been detected 13 (blueshifted lobe position angle (P.A.) ∼247 • ) perpendicular to the disk. Two bipolar lobes (cavities), cleared by the outflow, are illuminated by the central source and show up as reflection nebulae towards the southwest (blueshifted lobe) and northeast (redshifted lobe, see Fig.

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We present 0. ′′ 1 resolution near-infrared integral field spectroscopy of Hα in a z=1.4781 star forming galaxy, Q2343-BM133. These observations were obtained with OSIRIS (OH Suppressing Infra-Red Imaging Spectrograph) using the W.M. Keck Observatory Laser Guide Star Adaptive Optics system. Hα emission is resolved over a 0. ′′ 8 (6.8 kpc) x 0. ′′ 5 (4.3 kpc) region with a 0. ′′ 1 spatial resolution. We find a global flux of 4.2±0.6×10 −16 ergs s −1 cm −2 , and detect a spatially resolved velocity gradient of ∼134 km s −1 across the galaxy and a global velocity dispersion of 73±9 km s −1 . An upper limit of [Nii]/Hα 0.12 is inferred, which implies that this galaxy is not dominated by an active galactic nucleus and has a metallicity at or below 1/2 solar metallicity. We derive a star formation rate (SFR) of 47±6 M ⊙ yr −1 , and a dereddened SFR of 66±9 M ⊙ yr −1 . Two-dimensional kinematics for Q2343-BM133 fit well with an inclined-disk model, with which we estimate an enclosed mass of 4.3×10 9 M ⊙ within 5.5 kpc. A possible merger scenario is also presented, and can not be fully ruled out. We derive a virial mass of 1.1×10 10 M ⊙ for a disk geometry, using the observed velocity dispersion. We propose that Q2343-BM133 is currently at an early stage of disk formation at a look-back time of 9.3 Gyr.

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