Free Astronomy Magazine November-December 2020

50 NOVEMBER-DECEMBER 2020 SPACE CHRONICLES known as ‘standard can- dles’, which act as cosmic tape measures. Knowing the actual brightness of the supernova and observ- ing its apparent brightness in the sky, astronomers can calculate the distance to these grand spectacles and therefore their galaxies. Riess and his team com- bined the distance meas- urements from the su- pernovae with distances calculated using variable stars known as Cepheid variables. Cepheid vari- ables pulsate in size, caus- ing periodic changes in brightness. As this period is directly related to the star’s brightness, astronomers can calculate the distance to them: allowing them to act as another standard can- dle in the cosmic distance ladder. Riess and his team are interested in accurately measuring the distance to these galaxies since it helps them better constrain the expan- sion rate of the Uni- verse, known as the Hubble constant. This value accounts for how fast the Universe is ex- panding de- pending on its distance from us, with more distant galaxies moving faster away from us. Since it launched, Hubble Space Telescope has helped dramatically improve the precision of the Hubble constant. Results from the same observ- ing program led by Riess have now reduced the uncertainty of their measurement of the Hubble constant to an unprecedented 1.9%. Further measurements of NGC 2525 will con- tribute to their goal of reducing the uncertainty down to 1%, pinpointing how fast the Universe is expanding. A more accurate Hubble constant may uncover clues about the invisible dark matter and myste- rious dark energy, responsible for accelerating the Universe’s rate of expansion. Together this information can help us understand the history and future fate of our Universe. A supermassive black hole is also known to be lurking at the cen- tre of NGC 2525. Nearly every galaxy contains a supermassive black hole, which can range in mass from hundreds of thousands to billions of times the mass of the Sun. T his video shows a unique time-lapse of the supernova in galaxy NGC 2525. The supernova is captured by Hubble in exquisite de- tail within this galaxy in the lower left portion of the frame. It ap- pears as a very bright star located on the outer edge of one of its beautiful swirling spiral arms. This new and unique time-lapse of Hubble images shows the once bright supernova initially outshining the brightest stars in the galaxy, before fading into obscurity dur- ing the telescope’s observations. This time-lapse consists of obser- vations taken over the course of one year, from February 2018 to February 2019. [ESA/Hubble & NASA, M. Kornmesser, M. Zamani, A. Riess and the SH0ES team] P ictured here is the region surround-ing NGC 2525. Lo- cated nearly 70 million light- years from Earth, this galaxy is part of the constellation of Puppis in the southern hemi- sphere. [ESA/Hubble, Digitized Sky Survey 2. Ack: D. De Martin] !