This Hubble Space Telescope image is cluttered with myriad galaxies
NASA, ESA, B. Sunnquist, J. Mack, J. Lotz (STScI), HFF Team
The following is an extract from our Lost in Space-Time newsletter. Each month, we hand over the keyboard to a physicist or mathematician to tell you about fascinating ideas from their corner of the universe. You can sign up for Lost in Space-Time here.
If you gaze up at the night sky on a clear evening, chances are you will spot the constellation Orion, most likely recognizing it by the line of three stars that form its belt. These stars, named Alnitak, Alnilam, and Mintaka from left to right in the northern sky, may appear to have similar brightness to the naked eye, but this is deceptive due to their varying distances from Earth.
In terms of intrinsic brightness, the middle star Alnilam shines the brightest among the trio. Situated approximately 1340 light years away from Earth, Alnilam also holds the distinction of being the farthest.
Measuring such vast distances in the cosmos requires groundbreaking discoveries, such as the work of Henrietta Swan Leavitt in 1912, who identified a crucial relationship between the brightness of certain variable stars, known as Cepheid variables, and the duration over which their brightness fluctuates. By studying Cepheids in the Small Magellanic Cloud, a dwarf galaxy near the Milky Way, Leavitt provided astronomers with a way to gauge the absolute magnitudes of these stars.
Building upon Leavitt’s findings, astronomer Ejnar Hertzsprung calibrated the relation, estimating the distance to the Small Magellanic Cloud to be 30,000 light years, a milestone that sparked debates about the vastness of the universe and the nature of celestial objects beyond our galaxy.
Subsequent observations revealed a connection between the recessional speed of galaxies and their distance, leading to the formulation of the Hubble-Lemaître law, named after Edwin Hubble and Georges Lemaître. The law suggested a universe in expansion, challenging previous static models proposed by Albert Einstein and paving the way for new cosmological insights.
Over the years, advancements in observational techniques and technologies have revolutionized our understanding of the cosmos. Discoveries like the cosmic background radiation and the identification of dark matter and dark energy have reshaped our cosmic narrative, offering glimpses into the universe’s intricate workings and mysteries.
Despite these remarkable strides, discrepancies in measuring the Hubble constant, a key parameter defining the universe’s expansion rate, persist. Known as the Hubble tension, these variations in values derived from early and late-universe methods hint at the need for further exploration and possibly new physics to resolve the enigma.
As astronomers continue to unravel the complexities of the cosmos, the quest for understanding the universe’s expansion and evolution remains a captivating journey, offering tantalizing clues and questions that propel us towards new frontiers of knowledge.
