nyuusu wo kiite kouhunsita.

を marks ニュース as the direct object of 聞く.

So here:

• ニュース = the news
• を聞く = to hear / listen to the news

In other words, ニュース is the thing that was heard.

聞いて is the -て form of 聞く. Here, it connects 聞く to 興奮した.

A very common use of the -て form is to link actions or states:

• ニュースを聞いて、興奮した。
• I heard the news and got excited.

It can also imply a reason or cause:

• I got excited after hearing the news
• I got excited because I heard the news

So in this sentence, the -て form does more than just mean and. It suggests that hearing the news led to the excitement.

In Japanese, 聞く can mean several things depending on context:

• hear
• listen
• ask

In this sentence, it means hear or listen to, not ask.

Why?

Because ニュースを聞く naturally means to hear/listen to the news.
If it meant ask, the object would usually be something like a person or a question, not ニュース in this way.

So here, the meaning is something like:

• heard the news
• listened to the news

興奮した is the past form of 興奮する (to get excited / to be excited).

It is in the past because the sentence is describing a completed reaction:

• I heard the news and got excited.

Japanese often uses the past tense this way when talking about an event and the feeling that happened as a result.

Compare:

• 興奮する = get excited / be excited
• 興奮した = got excited / was excited

In this sentence, the speaker is talking about what happened after hearing the news.

Japanese often leaves out the subject when it is obvious from context.

So ニュースを聞いて興奮した does not explicitly say:

• I got excited
• he got excited
• she got excited
• they got excited

The subject is omitted.

In many situations, a learner will first understand it as:

• I heard the news and got excited

But depending on context, it could also mean:

• He/She heard the news and got excited

You need the surrounding conversation to know exactly who the subject is.

It can suggest both, and that is very normal in Japanese.

The -て form often covers ideas that English separates more clearly. Here it can mean:

• I heard the news and got excited
• After hearing the news, I got excited
• Because I heard the news, I got excited

The most natural interpretation is that hearing the news caused the excitement.

So the connection is not just two unrelated actions. The first part leads into the second.

Yes, it is grammatical and natural, but it is fairly strong.

興奮する means to become excited, often in a noticeable or emotional way. Depending on the situation, Japanese speakers might also choose other words:

• びっくりした = was surprised
• うれしくなった = became happy
• わくわくした = felt excited in an eager, happy way

So 興奮した works, but it gives a stronger sense of emotional excitement than some other options.

ニュース is a loanword, borrowed from English news, so it is written in katakana.

Katakana is commonly used for:

• foreign loanwords
• foreign names
• sound effects
• emphasis in some cases

So ニュース is the standard way to write news in Japanese.

Yes, but it changes the nuance.

• ニュースを聞いて、興奮した。
  = I heard the news and got excited.
  This describes a past event.

• ニュースを聞いて、興奮しています。
  = I heard the news and I am excited.
  This emphasizes the current state that continues now.

So:

• 興奮した = focus on the moment of becoming excited
• 興奮しています = focus on still being excited now

A comma is optional here.

You may see either:

• ニュースを聞いて興奮した。
• ニュースを聞いて、興奮した。

Both are fine. The comma just makes the pause clearer for the reader. In short sentences like this, Japanese often leaves it out.