The Hubble Ultra Deep Field (HUDF) is indeed one of the farthest and oldest images of the universe captured by the Hubble Space Telescope. It is an incredibly deep and detailed view of a small region of space. However, it is important to note that the HUDF is not the absolute limit of our observational capabilities.
There are a few reasons why we can't simply look beyond the HUDF to see even farther into the universe:
Observable universe: The universe is approximately 13.8 billion years old, and the observable universe is the portion of the universe from which light has had enough time to reach us since the Big Bang. The HUDF represents a view of the universe as it appeared when the light from those distant objects first reached us. Objects that are even farther away are beyond our current observable universe, as their light hasn't had enough time to reach us yet.
Expansion of space: The universe has been expanding since the Big Bang, and this expansion affects the light from distant objects. As space expands, it stretches the wavelengths of light, causing a phenomenon called cosmological redshift. This redshift makes the light from extremely distant objects shift toward longer, redder wavelengths. At some point, the redshift becomes so significant that the light is shifted beyond the visible range, making it difficult or impossible to detect with current instruments.
Instrument limitations: Even with advanced telescopes like the Hubble Space Telescope, there are limitations to how far and faintly we can observe. Factors such as the sensitivity of the instruments, background noise, and the accumulation of other sources of interference can impose practical constraints on our ability to detect extremely distant and faint objects.
To look deeper into the universe and probe even earlier stages of cosmic history, scientists rely on various observational techniques and instruments, such as the James Webb Space Telescope (JWST), which is designed to observe in infrared wavelengths and is expected to provide even more detailed views of the early universe.
Overall, our understanding of the universe's earliest stages is continually expanding as technology advances and our observational capabilities improve. Future missions and advancements in technology may allow us to explore even farther back in time and witness the previously unseen parts of the cosmos.