Based on two decades of radial velocity (RV) observations using Keck/HIRES and McDonald/Tull, and more recent observations using the Automated Planet Finder, we found that the nearby star HR 5183 (HD 120066) hosts a 3M J minimum mass planet with an orbital period of 74 +43 −22 years. The orbit is highly eccentric (e 0.84), shuttling the planet from within the orbit of Jupiter to beyond the orbit of Neptune. Our careful survey design enabled high cadence observations before, during, and after the planet's periastron passage, yielding precise orbital parameter constraints. We searched for stellar or planetary companions that could have excited the planet's eccentricity, but found no candidates, potentially implying that the perturber was ejected from the system. We did identify a bound stellar companion more than 15,000 au from the primary, but reasoned that it is currently too widely separated to have an appreciable effect on HR 5183 b. Because HR 5183 b's wide orbit takes it more than 30 au (1") from its star, we also explored the potential of complimentary studies with direct imaging or stellar astrometry. We found that a Gaia detection is very likely, and that imaging at 10 µm is a promising avenue. This discovery highlights the value of long-baseline RV surveys for discovering and characterizing long-period, eccentric Jovian planets. This population may offer important insights into the dynamical evolution of planetary systems containing multiple massive planets.

The large and diffuse galaxies NGC 1052–DF2 and NGC 1052–DF4 have been found to have very low dark matter content and a population of luminous globular clusters (GCs). Accurate distance measurements are key to interpreting these observations. Recently, the distance to NGC 1052–DF4 was found to be 20.0 ± 1.6 Mpc by identifying the tip of the red giant branch (TRGB) in 12 orbits of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging. Here we present 40 orbits of HST ACS data for NGC 1052–DF2 and use these data to measure its TRGB. The TRGB is readily apparent in the color–magnitude diagram. Using a forward model that incorporates photometric uncertainties, we find a TRGB magnitude of m F814W,TRGB = 27.67 ± 0.10 mag. The inferred distance is D TRGB = 22.1 ± 1.2 Mpc, consistent with the previous surface brightness fluctuation distances to the bright elliptical galaxy NGC 1052. The new HST distance rules out the idea that some of NGC 1052–DF2's unusual properties can be explained if it were at ∼13 Mpc; instead, it implies that the galaxy’s GCs are even more luminous than had been derived using the previous distance of 20 Mpc. The distance from NGC 1052–DF2 to NGC 1052–DF4 is well-determined at 2.1 ± 0.5 Mpc, significantly larger than the virial diameter of NGC 1052. We discuss the implications for formation scenarios of the galaxies and for the external field effect, which has been invoked to explain the intrinsic dynamics of these objects in the context of modified Newtonian dynamics.

It has been shown that ultra-diffuse galaxies (UDGs) have higher specific frequencies of globular clusters, on average, than other dwarf galaxies with similar luminosities. The UDG NGC 5846-UDG1 is among the most extreme examples of globular cluster–rich galaxies found so far. Here we present new Hubble Space Telescope observations and analysis of this galaxy and its globular cluster system. We find that NGC 5846-UDG1 hosts 54 ± 9 globular clusters, three to four times more than any previously known galaxy with a similar luminosity and higher than reported in previous studies. With a galaxy luminosity of L V,gal ≈ 6 × 107 L ⊙ (M ⋆ ≈ 1.2 × 108 M ⊙) and a total globular cluster luminosity of L V,GCs ≈ 7.6 × 106 L ⊙, we find that the clusters currently comprise ∼13% of the total light. Taking into account the effects of mass loss from clusters during their formation and throughout their lifetime, we infer that most of the stars in the galaxy likely formed in globular clusters, and very little to no “normal” low-density star formation occurred. This result implies that the most extreme conditions during early galaxy formation promoted star formation in massive and dense clumps, in contrast to the dispersed star formation observed in galaxies today.

NGC 1052-DF2 and NGC 1052-DF4 are ultradiffuse galaxies that have extremely low velocity dispersions, indicating that they have little or no dark matter. Both galaxies host anomalously luminous globular clusters (GCs), with a peak magnitude of their GC luminosity function (GCLF) that is ∼1.5 mag brighter than the near-universal value of M V ≈ −7.5. Here we present an analysis of the joint GCLF of the two galaxies, making use of new Hubble Space Telescope photometry and Keck spectroscopy and a recently improved distance measurement. We apply a homogeneous photometric selection method to the combined GC sample of DF2 and DF4. The new analysis shows that the peak of the combined GCLF remains at M V ≈ −9 mag. In addition, we find a subpopulation of less luminous GCs at M V ≈ −7.5 mag, where the near-universal GCLF peak is located. The number of GCs in the magnitude range of −5 to −8 is in DF2 and in DF4, similar to that expected from other galaxies of the same luminosity. The total GC number between M V of −5 and −11 is for DF2 and for DF4, calculated from the background-subtracted GCLF. The data are consistent with both galaxies having two GC populations: the one expected for their luminosity, and a very luminous population composing ∼90% of the total cluster mass. The number of GCs does not scale with the halo mass in either DF2 or DF4, suggesting that N GC is not directly determined by the merging of halos.

The ultra-diffuse galaxies DF2 and DF4 in the NGC 1052 group share several unusual properties: they both have large sizes1, rich populations of overluminous and large globular clusters2–6, and very low velocity dispersions that indicate little or no dark matter7–10. It has been suggested that these galaxies were formed in the aftermath of high-velocity collisions of gas-rich galaxies11–13, events that resemble the collision that created the bullet cluster14 but on much smaller scales. The gas separates from the dark matter in the collision and subsequent star formation leads to the formation of one or more dark-matter-free galaxies12. Here we show that the present-day line-of-sight distances and radial velocities of DF2 and DF4 are consistent with their joint formation in the aftermath of a single bullet-dwarf collision, around eight billion years ago. Moreover, we find that DF2 and DF4 are part of an apparent linear substructure of seven to eleven large, low-luminosity objects. We propose that these all originated in the same event, forming a trail of dark-matter-free galaxies that is roughly more than two megaparsecs long and angled 7° ± 2° from the line of sight. We also tentatively identify the highly dark-matter-dominated remnants of the two progenitor galaxies that are expected11 at the leading edges of the trail.