Revealing the Structure of the Universe
We know that visible universe is calculated to be 13.8 billion years old from evidence based on extensive studies using a plethora of techniques and technologies. The resulting prevailing theory is that the universe initiated with the “big bang” from which all matter, energy, and radiation in the cosmos was created. In this model, the universe expanded, first as a tremendous fireball of energy and later, as it continued expanding, was permeated with radiation and eventually coalesced into matter consistent with current observational evidence. The earliest matter seen by the Hubble Space Telescope was formed a few million years after the big bang event. HST has been used to sample the structure and the contents of the universe through a variety of observations.
The Deep Fields commenced with the Hubble Deep Field (HDF) in 1996 and include several other observing campaigns, such as the infrared Deep Field, the Hubble Ultra Violet Ultra Deep Field (2014), and the Hubble Deep UV (HDUV) Legacy Survey (2018). These Deep Fields have unveiled the details of evolving universe, track the birth of stars for billions of years, and document the cosmos’ busiest star-forming period, which happened about 3 billion years after the big bang. The latest comprehensive observations, combined with other space- and ground-based data, trace the universe’s evolutionary history.
The Deep Fields have been long exposures consisting of direct imaging of pencil beams probing the universe, dissected as “core samples” yielding information about the contents of the universe at deeper and deeper distances (earlier and earlier in cosmic history). To extend the detection capability of HST, gravitational lenses, created by massive clusters of galaxies, have been used to extend the reach of HST observations to earlier cosmological times. In addition, the Frontier Fields observations have served to refine gravitational lensing models, lead to a discovery of a background supernova and a prediction of its reappearance (confirmed), detection of ever more distant QSOs, and determination of galaxy morphologies early on in cosmological history.
Refinement of the Cosmic Distance Scale and Hubble Constant
A major goal of HST, as proposed for funding, was to determine the expansion rate of the universe and the implied age of the visible cosmos. With Hubble data, the expansion rate of the universe (H0) has been determined to better than 2.2% accuracy (astonishing since 10% was the goal). This rate, in 2018, is determined to 2.2% precision by combining HST and Gaia data. The value, or rate of expansion of 73.5 ±1.6 km/sec corresponds to an age for the universe of 13.8 billion years. While HST and other observations were used to create a robust distance ladder based on nearby parallax, Cepheid variables, and distant supernovae, the acceleration of the universe was uncovered resulting in the idea of Dark Energy. In addition, the ever-improving expansion determination has spawned intrigues in physics: besides Dark Energy there appears to be a “tension” between the HST+Gaia value and value determined by measuring the signature and ripples in the radiation from the Big Bang as well as theory.
Structure of the Universe
Determination of the structure of the expanding universe, that is the Cosmic Web, requires numerous diverse types of observations. Spectroscopic observations with HST’s Space Telescope Imaging Spectrograph (STIS) and the Cosmic Origins Spectrograph (COS), coupled NASA's Far Ultraviolet Spectroscopic Explorer (FUSE), revealed that hot gas, mostly oxygen and hydrogen, could be used to map three-dimensional nature of intergalactic space. Filaments of oxygen and hydrogen superimposed on bright quasar light trace large quantities of invisible, hot, ionized hydrogen that are too energetic to be seen in visible light, yet too cool to be seen in X-rays.
Galaxy Assembly and Black Hole Cores
HST observations have been used to examine aspects of the assembly of galaxies in the universe, as well as the formation of galaxy clusters, and large samples of merging galaxies. Surveys of large samples of these objects suggest a model for the merger rate as a function of time in the universe and how morphology is influenced by galaxy interactions. The investigation of merging galaxy nuclei has been fundamental in understanding how black holes form and how enormous amounts of energy can be unleashed through colliding black holes. These events are candidates for the production of gravitational waves, and the understanding of the incidence of such mergers can be a predictor for multi-messenger observational strategies.