The Problem of an Expanding Universe

A new, precise measurement of the expansion rate of the Universe is in, and it's serving up a huge cosmic pickle.


Using Hubble data and new observations from the James Webb Space Telescope (JWST), a team led by physicist Adam Riess of Johns Hopkins University has confirmed that previous measurements are correct after all, despite years of debate.


Based on immense distances from our Solar System to Cepheid variable stars and Type Ia supernovae, which are used to create a 'cosmic distance ladder', our Universe does indeed appear to be expanding at 73 kilometers per second per megaparsec – a rate known as the Hubble constant.  READ MORE...

A Vast Galactic Neighborhood

This image from the NASA/ESA Hubble Space Telescope features a richness of spiral galaxies: the large, prominent spiral galaxy on the right side of the image is NGC 1356; the two apparently smaller spiral galaxies flanking it are LEDA 467699 (above it) and LEDA 95415 (very close at its left) respectively; and finally, IC 1947 sits along the left side of the image.


This image is a really interesting example of how challenging it can be to tell whether two galaxies are actually close together, or just seem to be from our perspective here on Earth. A quick glance at this image would likely lead you to think that NGC 1356, LEDA 467699, and LEDA 95415 were all close companions, while IC 1947 was more remote. 

However, we have to remember that two-dimensional images such as this one only give an indication of angular separation: that is, how objects are spread across the sphere of the night sky. What they cannot represent is the distance objects are from Earth.     READ MORE...

A Dangerous Dance Miles Away

Hubble Space Telescope image of Arp 91, a pair of intertwined galaxies (NGC 5953 and NGC 5954). Credit: ESA/Hubble & NASA, J. Dalcanton, Acknowledgement: J. Schmidt

This Picture of the Week features two interacting galaxies that are so intertwined, they have a collective name — Arp 91. This delicate galactic dance is taking place over 100 million light-years from Earth, and was captured by the NASA/ESA Hubble Space Telescope. 

The two galaxies comprising Arp 91 do have their own names: the lower galaxy, which in this image looks like a bright spot, is known as NGC 5953; and the ovoid galaxy to the upper right is NGC 5954. 

In reality, both of these galaxies are spiral galaxies, but their shapes appear very different because they are orientated differently with respect to Earth.

Arp 91 provides a particularly vivid example of galactic interaction. NGC 5954 is clearly being tugged towards NGC 5953 — it looks like it is extending one spiral arm downwards. It is the immense gravitational attraction of the two galaxies that is causing them to interact. 

Such gravitational interactions between galaxies are common, and are an important part of galactic evolution. Most astronomers nowadays believe that collisions between spiral galaxies lead to the formation of another type of galaxy, known as elliptical galaxies. 

These immensely energetic and massive collisions, however, happen on timescales that dwarf a human lifetime — they take place over hundreds of millions of years. So we should not expect Arp 91 to look any different over the course of our lifetimes!

The Einstein Ring

The Hubble Space Telescope captured a stunning ‘Einstein Ring’ 3.4 billion light-years from Earth.

This cosmic display, formally known as gravitational lensing, occurs when the gravitational field from a massive object in space warps space and deflects light from a distant object behind it.

It then results in a bull’s-eye pattern, or ‘Einstein Ring.’ It was predicted by the famed physicist, Albert Einstein, in 1915.

The image shows six luminous spots of light clustered at the center, four of which are forming a circle around a central pair.

The formation, however, only consists of two galaxies and a single distant quasar that is magnified as it passes through the gravitational field of the galaxies.

The Hubble Space Telescope captured a stunning ‘Einstein Ring’ 3.4 billion light-years from Earth

The quasar, known as 2M1310-1714, sits farther away from Earth than the pair of galaxies.

A quasar is the extremely bright nucleus of an active galaxy and its powerful glow is created by the incredible amounts of energy released by gas falling toward the supermassive black hole at its center.   READ MORE

A Dying Galaxy

From the smallest microbe to the mightiest oak, death is as true for above as it is for below, even for the mightiest galaxies.

The process, however, is not a quick one. A haunting new Hubble photo of the galaxy NGC 1947 demonstrates this well: Even from a distance of around 45.4 million light-years away (in the southern constellation of Dorado), we can see that the galaxy is slowly on the decline.

The clue lies in the dust and gas. A galaxy in the prime of its life will be filled with the stuff, using it to make new stars. Eventually, the star-stuff will run out, and that's what astronomers believe we are seeing with NGC 1947.

It's a rare type of galaxy known as a lenticular galaxy - disk-shaped, like the Milky Way or Andromeda, but without the spiral arms. NGC 1947 used to have spiral arms, but it has used up almost all the gas and dust that gave them structure; all that remains is a few wisps, backlit by starlight.  Read More