Calculating the distance to far-away objects, such as galaxy clusters and quasars, is difficult. But it is also critical to our understanding of how the universe evolves. Luckily, humanity has a trusty workhorse that has been collecting data for such calculations for decades—Hubble. It is by far the best telescope suited to the job, as described by a recent NASA press release about a distance measurement to a supernova in a nearby galaxy.
The NGC 3810 galaxy is a spectacular example of a spiral galaxy in the Virgo Supercluster, which had a Type Ia Supernova happen late in 2022. Hubble began observing it in 2023, and some of that data was used to create an absolutely stunning image of the galaxy, as seen in the header image.
Calculations showed that the galaxy is about 50 million light-years away and around 60,000 light-years across. But how did Hubble arrive at those numbers? It used the unique physics around Type Ia supernovae.
Type Ia supernovae happen when a white dwarf explodes, but importantly, the absolute magnitude of each explosion happens with little variation. Each Type Ia supernova is expected to produce about 5 billion times brighter light than the Sun. And since there is hardly any variation in that brightness level, astronomers can use the brightness we observe on Earth to calculate the distance the light traveled to reach us.
That seems simple enough, but there is one confounding factor—intergalactic dust. While on their own, these sparse particles of matter in the intergalactic voice might not seem like much, when taken as a whole, they can significantly dim the light from a far-away supernova.
However, that is only the case in certain wavelengths. For example, in ultraviolet light, the light from a Type Ia supernova is almost completely absorbed by the dust. In contrast, in infrared light, the light almost completely passes through. Hubble is still our only functional space telescope capable of seeing in both wavelengths using a single instrument. Not even the James Webb Space Telescope can do that.
Using the difference in data from the ultraviolet and infrared bands on Hubble, astronomers can calculate the brightness of any given Type Ia the telescope can look at, thereby providing a rough estimate of the distance to that supernova and its host galaxy. It’s always good to counter-check a distance measurement, though, and in the case of NGC 3810, astronomers used a technique that calculates the distance by comparing the rotation speed to its brightness. That result confirmed the estimate that the galaxy is about 50 million light-years from Earth.
Unfortunately, in the future, these measurements will not be as easy for Hubble to complete. This data set was collected during 2023, but as we reported more recently, trouble with the telescope’s gyroscopes is forcing it to slow down some of its observations. Given the fleeting nature of Type Ia supernovae, that slower speed could impact its ability to provide this critical data to astronomers.
Until then, we will have to rely on simultaneous measurements from telescopes like JWST, though there currently isn’t any space-based telescope other than Hubble that can take ultraviolet images. NASA’s planned Ultraviolet Explorer mission will do so, but it isn’t scheduled to launch until 2030. So, soon, Hubble will remain our workhorse for this particular astronomical measurement, no matter how much it might be slowing down.
Learn More:
NASA – Hubble Measures the Distance to a Supernova
UT – Uh oh. Hubble’s Having Gyro Problems Again
UT – Hubble’s Back, but Only Using One Gyro
UT – This Galaxy Hosted One of the Most Powerful Supernovae Ever Seen
Lead Image:
Image of galaxy NGC 3810, including the supernova that led to the estimation of its distance 50 million light years from Earth.
Credit – ESA/Hubble & NASA, D. Sand, R. J. Foley